Whether traveling with a dog or cat, the first thing to realize is that all animals have distinct personalities. Some personality traits can be modified through training, but some will be hard wired and can't be changed. It will be the personality of the animal that will inform you about whether they will be a good travel companion.
We had friends in Boise who traveled with their cat, which they had always had as an indoor cat. That required a large RV because they had to have room for the litter box.
In general, most dogs make better travel companions. They are more easily trained and they are pack animals - sleeping in a teardrop with the owner(s) to them is like snuggling up with their litter mates when they were young. Dogs are wired for that scenario, so they love it. Cats are more aloof and will want some place to get away from you. And my experience is that it is a bad idea to have an unhappy cat.
With dogs you need to understand that there is a continuum of energy levels, and most breeds generally can be classified as low energy, medium energy or high energy. A low energy dog like a Lhasa Apso won't require much of your attention and makes a great lap dog. A high energy dog like a Jack Russell Terrier will require a LOT of attention, and they are masters at manipulating their owners.
For us, a medium energy dog makes a great travel companion. Lana is pretty low key except for about an hour every day, late in the afternoon. Then she's full of energy. If left on her own she would go blasting through the woods at full speed for about a half hour, jumping over and around obstacles and perfecting her high speed turns. With that need accommodated every day, she's content to lay around all day or go hiking all day. When not being active, she only needs her ball or a bone to keep boredom at bay.
I wouldn't recommend becoming a first time pet owner while living in a camper of any size. You'll want to know that your pet will always want to be with you before you go on the road. Otherwise, the first time they get loose could be the last time you see them.