Putting radiant heat under carpet is very inefficient. They do make special padding that does transfer the heat better.
I have whole house hydronic radiant floor heat in my S&B home. I would never consider building a new house without it. But I would never put it in an RV unless you just leave it parked at one location.
As said earlier it takes a long time to heat the space and if you don't have the proper outdoor temp controls installed it will then overheat.
The electric mats are OK to warm a small area like the bathroom floor.