We full timed with 2 cats in our Jayco fiver covering 44 states back in 92-94 during what we called our sabatical. One was 5 and one 12. They loved it and also were a great help in determining what was outside our 5th wheel at night! When they ran from the screen door we made sure we had a campfire if we sat outside to look at the stars.
Currently have 3 siamese one is 1yr, and (2) are 11 yr olds... and they love to camp. We modified the washer/dryer area for the litter box, for privacy... complete with carpet to help contain the litter and a 12 volt light so clean up is easy. They ride in our fiver and seem comfortable enough and look forward to treats and fresh water when we stop for fuel....meeting us "at the door".
I saw a great screened in cat porch last time out. It unfolded to 6 feet long and 24" x30" that the owner set up on saw horses and then connected to the basement which he modified to connect to the living area. The 2 cats could go and come as they wanted to and of course it had a vinyl roof to keep the sun and rain out. Saw them enjoying their cat naps on their porch. I'm going to come up with a plan to do the same thing!
"Down the Road"
Doug and Donna & our 3 Siamese
2006 Ram 2500 Mega Cab HD 2 WD w/Cummins TD Pull-rite Super slide
2012 Eagle 321 RLTS with MOR/ryde pin box