FWIW, I have my MH just so I can go places with my dogs ? mostly upland bird hunting in remote area of the west. Any working dog must travel happily because they cover tens of thousand of miles/year and mine are no exception, but they like MH travel the best because they have the most room and they can really see out the big one-piece windshield. They have the run of the place, but generally I turn the big leather passenger chair around to face the front when I am actually driving and they sit there and watch the world go by. They are with me during the day, just like at home; and at night, they sleep at the foot of the bed, just like at home.
Generally they are out with me when I am out, but if I must leave them, I have no hesitation. They just wait quietly in the MH for me to return.
Bottom line ? mine just love MH travel, even though when they get in the MH, they don?t know if they will be gone a couple days or a couple months, driving for a few hours or several days, etc.
If you dog likes to travel in the car, I?m certain there will be no problem in the MH.
The only problems I have found are these:
1. My dogs need to run hard, off-lead, for miles every day to stay fit and happy (and so does the Old Man). Campgrounds have very restrictive rules when it comes to dogs (and lots of Rules Nazis to enforce them). I do understand the reasons for the rules in such crowded places, especially since most dogs seem to be poorly trained/controlled, but I do not like them. One of the universal rules is dogs must be leashed at all times (never mind that mine handle far better off-lead than on-lead), so it is impossible to attain the needed levels of daily exercise at a campground. But usually we avoid campgrounds when we can; and even when stuck in a campground we can often hop in the toad and find a place where we can run. When they are actually working (hunting) this is no problem of course, as they will cover about 45 miles/day.
2. My dogs are kept in an ex-pen when we are ?camped? so that they can enjoy the scents and people going by, so they don?t bother anyone, but they are visible and exposed to campground busybodies coming on to my site uninvited so their little foo-foo dog can ?play with the nice doggies?. My dogs are bred and trained to dispatch small varmints (a very useful thing for a rural landowner like me), but only on command (because I don?t ever want my dogs taking on some critter without my knowing and allowing it). To my dogs, a yipping toy dog is a ?small varmint?. While they are well-trained and have never broken their training in this regard, when someone has their tiny dog stick its head in my dogs? pen, I get concerned - if there was going to be a problem it would happen before the busybody could blink. So, I must instantly stop wherever I am doing, leap up and try to get the busybody and her dog to leave without upsetting her.
Cats in an RV? I know people do that, but I can tell you that I leave my elderly cat at home ? I think she would HATE the MH. My suggestion would be to start with a kitten and not subject an older cat with health problems to the stress of travel. FWIW, my cat is also hyperthyroid and has been for maybe five years ? she does fine as long as she gets her twice daily meds.