Saw a really neat homemade one a few years ago, wish I had taken pictures. They used 110V AC motor so they could just plug in when they were close enough but built it with a spot to mount a small generator (in their case it was a Honda 2000i). Now they had all the advantage of a battery operated unit but with fewer things new they had to buy since they used the Honda for their trailer and most pack rats have a large enough AC motor laying around. They actually made it so they could take it along with them when camping to move the trailer into tight spots.