A-B-C class you'll definitely want a big block SOMEthing, gas or diesel. They'll have to work a HELL of a lot less than ringing the life outa small block.
My 'Gearhead Motel' is a 24' C class '77 Dodge with 440/727, Edelbrock/Edelbrock, RV cam, deep trans pan & cooler. I pull an 18' open and it all cruises along just fine. It's an overhead main bed and a bunk bed in the rear where I pile in tools-parts-gear. It ain't as luxurious as a class A but it works for lil' ol' me ! If ya take a group with you a class A is the way to go.