Campers often aren't very well insulated so I would also be concerned about ambient temperature swings. If you're going to use tubs use two UTH's on each one. One set should be set 90-92*F, the other 80-82*F. If it gets too hot the low side UTH's will simply cut off, and if your ambient drops because it still gets pretty darned cold at night then with both sets of UTH's active your snake should stay warm enough.