The idea of charging 12 volt, is very fuel efficient. As it doesn't need to idle, to handle the load. Maybe if they take the self-start out, it would be under $400. LOL
Propane is a nice touch, more common on 4 strokes. But aren't they a little pricey too?
20amps x 14.5volts = 290watts / 756 = .38 hp In a perfect world.
I'm thinking of adding a 12volt 50amp alternator to my $150 genset. Got the alternator and nohow, just lacking a little skill.