We have electric heated floors in our home. In the Kitchen and Living room under tile. It is a great way to take the chill off and keeps the room warm. We actually had to turn them down because they effect the whole house heat and wouldn't allow the heat to come on in the rest of the house.
I think they would work in an RV assuming you have a constant power source. If you were using it off grid, it would be a no go. Which is probably one of the reasons RV manufactures don't waste effort putting them in RV's. Most heat sources are inexpensive to put in, like a propane furnace or small fire place electric heat. I think if you were doing a remodel and changing the floors, it wouldn't be a bad investment assuming you always had power and could put them under hard floors. Radiant heat doesn't work under carpet.