No matter what the cats are used to at home, traveling is a different scenario. Our indoor cat is unfettered at home, but she wears a collar (tags attached) and harness when we're traveling with her, and a leash when we're in the truck, or when she just gets into the camper (or is just going to be taken to the truck), even though she is also zipped up in her carrier. I bought a soft-sided small-dog carrier for her - there's more room for her to sit up, turn around, etc. than in a standard cat carrier, and more comfortable for her in the truck. We carry her in that from truck to camper and back again. She's an indoor cat at home and is also an indoor cat in the campsite, though at times she begs to come outside with us. (We can resist the begging. :) )
Other advice - as with dogs, rabies shots and verification of them may be needed, as perhaps other shots (not usually so much with cats, though). And our cat is microchipped.
Other than that, go with what makes the cat(s) most comfortable. MHs offer the most comfort for those home-loving animals, since their home and vehicle are the same, but for safety you may want to confine them to carriers while on the road anyway. Of course it goes without saying that if you have a trailer, the cats will need to ride in the TV with you and not in the trailer! If they are anxious while on the road, some Feliway pheromone spray may help calm them. Make sure they know where the litterbox is and stick with familiar litter, food, etc. Because of changes in water tastes in different areas, we have kept our cat on bottled water.