But you have to have 12v wiring going to the use area that will maintain the voltage needed at the amps needed
And many of these products only supply the stated heat level
When the engine is running and the alternator is supplying 13+ volts
What might be practical in a van
Is not so useful in a larger RV, like my 36ft rear bedroom class A
The amount of heat desired/needed various with the individual
I sometimes use a heat pad on my back before going to sleep
But again this is my home, not for my weekend use to play in the snow