Until this year we have never had anything living in the travel trailer when on the road. Everything rode in the tow vehicle (truck). That is until this year (well, December 2014).
Our cat cannot take riding in the truck. He gets himself so worked up he vomits and (looses it at the other end too). We've tried everything. Well, last December for our Christmas week trip to Florida, we left him in the trailer. He's very familiar and comfortable in the trailer. He has his favorite spot. A little cubby hole at the head of our bed. He crawls in there and that's his "safe spot".
Well, we couldn't take him making a mess in the truck, in a cat carrier, loose in the truck, holding him, nothing. But in the camper, he immediately settled in his little cubby hole. Well, we experimented and in the camper he has his litter pan, no vomit, no mess, no nothing!
Our last trip to Florida (last week), we let him ride in the trailer both ways from Indiana to Florida (3 days driving each direction), and he did wonderful! When we stopped, we'd check on him. He'd pop his head out of his little cubby hole and come out, happy, snugglie, want to be petted, and then he'd go back. It worked perfect for the 6 days of driving we did!
Our dog HAS to ride wherever we are. If we attempted to put the dog in the camper without us, even traveling, he'd go nuts in there! We can't leave him in the camper alone when we're parked! He goes bananas! He wants to be with us.
So to answer your question ... we normally never let anything living ride in the camper, until just recently! Dog in the truck, cat in the camper. It works for us now.