Typically, no, there is not an inverter as standard equipment. Some are including them as part of the residential fridge upgrade, but doubt they are big enough to use for other purposes. One could always be added with a little work.
As far as too big, you are correct that it is a concern, however most National Parks dont allow OHV use. National Forests do, and spost will tend to be on the small side. I would expect that you will have to uload the toys before backing into your spot. Places in the SW will tend to be much more open as will ATV/SxS catering areas like Hatfield/McCoy.