First Time (ish) RVer and Toad

Hey all
So my family and I will be going full time RVing for a year while we are in a transitional phase.
So that being said, we are in the market to purchase a class C.
However we are going to need to tow our 2015 Prius C preferably on a trailer or possibly a dolly that won?t need adjusting as we drive (I?ve heard tales of some where straps come loose as you drive).
GVW for our car is 4,300lbs (including an approx payload). Curb weight is 3,340lbs.

We looked into diesel class C?s but they are either out of our price range or are smaller than we need.

So my question is, would a gas class c safely tow our vehicle? Or rather, what specific things should we look for to find a class c that will safely tow it?
We have family in WVa so we will definitely be going up hills and mountains.

Many larger Class C should be able to tow the Prius.  It WILL require a tow dolly or trailer.  Bad news is all dollies need the straps tightened initially, again in about 10 miles, and then checked every 100 miles or so.  It simply comes with dolly towing.  Sorry.  If you carry it on a car trailer with all 4 wheels up, the tie downs are different, and should remain tight better.  It also provides more space to carry "stuff" without adding weight to the RV.

Weights get tricky, though.  Every RV will have maximum cargo carrying capacity weights, max towing weights, max hitch weights, Gross Combined weight of the RV and all towed items, etc.  Do some serious reading here on the various threads, in our Library (click the icon near the top of the page), and any other source you find. 

ASK LOTS OF QUESTIONS!!  That is why many of us are here, to help you do it right and stay safe while enjoying this great country.

So you think you are going to put your family in an class C RV and tow a Prius on a trailer? You will be massively overweight with just about any C you can find. They don't have much cargo carrying capacity, which is what you are going to need in spades for a year of full timing with that crew. My suggestion is to find a a 35 foot class A such as this one:

https://www.pplmotorhomes.com/used-rvs-for-sale/class-a/2003-national-rv-dolphin_rv-39316

Grashley,
Number crunching is something I?ve been doing like crazy. Posted on here because I just can?t find solid info on towing. Some say yes, some no, and a lot of ?yes..but?s? lol.
I?m not sure if this matters but I do intend on removing the couch and changing the water heater to a tankless. I figure those two things should save weight a bit.

I?m also toying with the idea of trading in the car for a good capable truck and buying a fifth wheel.... I just REALLY like my car though. The gas mileage is beautiful. Ha!

SeilerBird,
Class a won?t really work for what we need and still be within budget. It?s just me, my husband and daughter.. but she needs a dedicated sleeping space (like the class c?s over cabin bunk). Somewhere for her to have some quiet alone time when she needs it. More importantly a little space that?s just for her.

Looked at class a?s with a bunkhouse but ultimately weren?t thrilled with the general layouts of them from what I saw. Plus class c?s seem to be easier to work on should the need arise.

Thanks for the information.  I was imagining 3 kids stuck in there for 3 solid days of bad weather!

To answer your more specific weight questions, since you have crunched enough numbers for this to (hopefully) make sense.

Every RV will have a "few" weight ratings associated with that rig.
GVWR is the most the fully loaded rig can weigh with all your gear loaded.
Curb wt is how much the empty coach weighs with only a full tank of fuel.
GVWR MINUS curb wt = how much weight you may add, or CCC - Cargo Carrying Capacity.
Removing the couch and changing water heaters WILL change Curb wt. and CCC.
If the propane tanks were full when it was weighed, then propane need not be included in CCC

GCWR is the max weight of the loaded rig and anything being towed.  Here is where it can get confusing. 
FOR EXAMPLE, assuming an RV Curb wt of 17,000# GVWR of 20,000# and GCWR of 25,000#,

You can load 3000# of stuff into the RV and still tow 5,000# of Prius and tow dolly.
You can load 2,000# of stuff and have 6,000# of Prius, car trailer and other stuff on the trailer.
You CAN NOT load 4,000# of stuff in the RV (RV overloaded) and 4,000# of Prius and dolly.
Remember to include the hitch weight of the towed in the RV  GVWR.  Also check the hitch capacity.

The real answer to your towing question lies in the actual weight rating of the RV in question.  Some smaller Class C may not make it.  Larger Class C gas should be acceptable.  While the numbers may say yes, do not expect to maintain 60 mph going up W VA hills!  The diesel is clearly more powerful (torque at lower rpm) pulling the hills, and, as you already know, more expensive.

Some other questions come to mind.  By your last post, I suspect you have already considered these items.  I do not need answers, but you should consider them!
1.  Do you have income to cover this year?  RV life is NOT cheap!  Many campgrounds with full hookups run $25 - $40 per night.  At $35 per night, that is $1050 per month campground fees.  Driving the RV at 7mpg can get expensive, too!  There WILL be RV maintenance costs as well.  You still need to cover food, clothing, medical, ...
2.  I assume you are currently in a home / apartment.  What do you plan to do with the 80% of your stuff you can not carry with you?
3.  It sounds like you plan to "rent" the RV for a year, then sell it and move back to a brick and mortar home.  I strongly suggest buying gently used.  If you go new and finance the rig, a year from now, you will owe significantly more than it is worth.
4.  If you have never gone RVing before, I suggest renting a Class C about the size you want to buy for a week.  It will be worth every penny!  You will quickly learn if this is do-able for your family.  You will learn if this size will work.  You will fine tune your floor plan needs in a way nothing else can do.  You will come up with a whole new list of questions.
5.  I assume you will be home schooling.  Make sure your floor plan will fit this need.
6.  Lock the 3 of you into the camper you want for 4 hours.  Check all seating and sleeping positions for comfort and privacy.  Is the bathroom / shower big enough?  Is the kitchen workable for a year of meal preps?  After ONLY 4 hours, are you all still comfortable, or ready to escape before you kill each other?

The truck / FW option is possible.  I spent $40K for a 3 year old NICE truck (see my sig) and $26K for my FW.  Plan on another $5k for fixing it your way.  You do not need to spend quite that much, but it can give you an idea...
Compared to the Class C, you will love the fuel economy when towing, and hate the mileage when not towing.

I hope this clears the water more than it stirs the mud!  Keep asking questions!