My hybrid has never been without power. I keep it plugged in on a 20A circuit 365 days a year. I was told yesterday by a motorhome owner that it was not good to do it, although he did not give me any ...
If you have a good three (or four) stage battery charger (often called a "converter") that is maintaining the batteries, there should be no harm. If you have one of the cheap pieces of junk converters that come with so many RV's, then you will likely boil your batteries. At a minimum, I suggest you check the battery water frequently until you determine how quickly it is going down.
I agree, it nice to have a little place to go and relax....and pretend to be camping :)