Oh soooo many questions

My wife and I are thinking about buying an MH. 

We have never slept in one or really been around one other than going to an RV show.

Because I don't own a truck, and I have 2 in the family that will need a bathroom 20 minutes after a stop, I am thinking a class C, or maybe an A.  I have 3 kids, wife and a German Shepard. 

I am looking for a used unit, but I don't know what I don't know about these things.

I am somewhat handy with a wrench and I know some basic plumbing and electrical.

I am leaning towards a Winnebago because of all the posts and threads I have read.

Any advice?

I'd do this math:
You + Wife + 3 Kids = 2 Bathrooms

Don't rush into one. Keep looking around to learn what is available and what features suit your needs.  This is like choosing and buying a fully furnished house, so forget the car-buyer mentality. Focus on the layout, space, storage for clothing & gear, usability of the galley, etc. And the condition of everything.

We have RV buying checklists in the forum Library, for when you get down to that stage.  Sadly, the buying experience IS all too much like buying a vehicle, i.e. the proverbial used car sales lot. Most RV salesmen will tell you anything they think you want to hear, and few of them are actually very knowledgeable about using Rvs. They know how to make a sale, though!

With 5 people and a large dog, you will want a lot of space. And maybe a second pottie as well. You are probably in class A territory, since an A is far superior to a C in any length over about 29 ft.

Welcome to RVForum!  There are so many people here who have years of experience.  It has helped time and again when I felt stuck or needed some simple advice.

Gary RV Wizard is right in his advice. My advice is to leave your wallet and credit cards at home and go shopping at dealers and RV shows to look at a wide variety of Class Cs and Class As and figure out what is the best floor plan for your family's needs.  While Class As are often bigger, Class Cs can sometimes sleep more people.  Are there enough beds? bathrooms? Do you need a pass through to the rear bedroom? Do you want multiple slideouts? Is there room at the table for your family to eat?  Do you want an outdoor kitchen?  As Gary said an RV is more of a place to stay in than a vehicle so focus there first?  Once you narrow the search to what you want you can pick the brands and models that meet your needs.

Most people here will tell you to look for something that is a few years old.  I will tell you the same.  Every RV has things wrong with them and need to be ironed out by the first owner.  Don't think that the dealership will make these quickly go away like they do in your car.  Accept that RVs are more like boats than cars and will requires some personal attention and buy one that someone already debugged.

Then go on RVTrader.com and search for the ideal RV and see if there is one you like nearby.  If nothing else it will calibrate you on a fair price for the model you want.  Good luck!

Unless you plan on using full hook-up sites all the time or are willing to use the campground facilities, you will need to pay attention to the fresh, gray, and black tank sizes. That may make the difference between an A or a C. Depending on the age and mindset of the children, you may also consider them using their own tent, at least part of the time.
  As far as Winnebago goes, I have nothing against them, and if I were looking for another RV I wouldn't rule them out, but I haven't seen where they're any better than anything else in their price range. One big plus for Winnie though, is the factory service and support. But then again, I have received great factory support from Coachmen.

When looking at rv's consider where everyone will sleep and if you have to crawl over each other for all those potty breaks.  Personally, I want a clear path.  Also,how old are kids and how soon will they need real beds?take the time to fold down the beds and find out if they fit.

Think of all the cooking gear you might want to haul.  Toaster,coffee machine,crockpot.  How much storage for that AND your actual food?  What about bikes,a tent, beach gear,chairs?  It can fill up fast! 

Good luck in your search!

True enough about the class A being superior in many ways, but I'm not so convinced in the smaller low end ones.

but you and I, with three kids, are in a bit of a niche market where a C is in some ways better.

Some A's do have a motorized bunk that lowers down over the driver's seat, and some have bunks...but it's hard to beat that overhead bunk in a C.
We really like our floorplan and it is still working well enough for us.  I was originally searching for a bunk bed plan, but they have downsides too.  When my kids were smaller all three would comfortably sleep in the overhead.  Now we almost always have one on the couch.  They don't mind.

Most C's, like mine are on the verge of being overloaded, and they have limited tank capacity.  For me, my grey tank can be a limiter....but it's enough for our typical weekend type trips....and we did well on a recent 19 day 5,200 mile trip too.

If budget wasn't so much an issue, I'd look at the super C's.  The ones Thor make on the F-550 chassis aren't quite what the really big ones are, but I feel like they would fix many of the limitations I have with mine.

And don't forget your furry kid's needs that include a bed, toys, bowls, and lots of food!  Most new RVers underestimate how much everything weighs (think tools, canned foods, drinks, etc.) so you need to look at the weight of the rig.  For example, if you only have 600 pounds carrying capacity the people and dog will take a good portion of that amount without much left for what you'll all need to carry.  Do check in our RV Forum Library (button above left) to find explanations of everything related to RVs and written by our own members.  You also might consider renting an RV and taking a short trip to get an idea of how things work, as well as how you'll all fit into an RV, regardless of the type.  If nothing else, it will help you figure out what you need and don't need.  Have fun looking!

ArdraF

There has been a lot of good advice so far, but as you said you don't know what you don't know.  One good example of this is many people look for cargo carrying space in an RV, but forget to look for cargo carrying capacity, meaning having a lot of cabinets is not a big help if you are within a few hundred pounds of your chassis weight limit.  It also helps to have an idea of how you plan to use the RV, and how realistic that plan is, do you foresee big trips, or weekend outings to the nearby lake, at full hookup campgrounds, or boondocking in the middle of nowhere, do you live in a part of the country where RVing is summer season only affair, or is it closer to year round? 

You have already said you are shopping for a used coach, I would suggest setting some parameters on how old you are willing to consider, and what your purchase budget is while keeping some money in reserve to deal with unexpected issues, almost all used motorhomes have some, either service issues that fell through the cracks, or updates that may be important to you that were not important to a previous owner (Tire pressure monitors, GPS nav systems, updated entertainment system, mobile data, or maybe it is suspension updates to make it drive better, or perhaps the previous owner was great about keeping up the cosmetics, but did not notice that the shock absorbers were shot)

When I was shopping for my first class A last year, I set my absolute oldest age I would consider as 1996, assuming a gasoline powered engine, this is because 1996 was the first year the US government mandated the OBD-II diagnostic interface, and it is hard to find a mechanic these days that know how to work on anything that does not have one.  I also set my preferred model years as being something newer than about 2001, my reasoning was this was the introduction date for the 8.1L Chevy Vortec engine in Workhorse chassis motorhomes which had 50 more HP and 45 more LBS/Ft torque than the preceding 7.4L, (the beginnings of the modern Ford 6.8 V10 dates from about the same time) also I feel most post 2000 motorhomes have a more contemporary paint color scheme than most 1990's models (more earth tones, less cream color based, and no teals and purples that were common in the late 90's that now look as dated as mustard yellow from the 70's.

I too am a newbie and have not bought yet.  But what we did to is rent. Which helped answer what we wanted, what would work and what didn't. We did know wanted a Class A so that's what we rented.

We just upgraded from a 25 foot TT with bunks but no slides to a motor coach about a month ago. We are in a very similar situation to the original poster in terms of kids and dog.

I think you need to spend time with the family in a camper of any kind to figure out what will drive you batty. You can't take a dog to most rental campers, but if you have the amount of experience in a camper it sounds like, it's worth getting whatever you can. Lots of campgrounds have campers you can rent for a couple nights.

I spent close to a year researching online once we decided a motorcoach made more sense than a newer and larger TT. (What we thought we wanted changed quite a bit and we thought we would go for a small Class A for a long time.) We knew what we wanted from experience of using ours, which helped me eventually determine there was no class A out there we could afford and were willing to drive that had a floor plan that was family friendly. The choice between class C and A for us came down to the length we wanted and a strong knowledge of the layout we needed inside.  We then put many hours of actually climbing into them in dealerships across the country. It didn't take long to know we had the right one for us when we were ready to buy.