I do not see why you could not grow in a RV.

There are skylights that you can install. If you are using lights you just plug into the electricity of the place you are staying at.

If you were vegetating you would be stuck where you are at. If flowering you would just drive during your dark period. I suppose you could get a generator.

But if you get pulled over buy a cop it would be kind of hard to stay you were just holding the grow for one of your friends.