It’s there a 120v actually to 72v dc adapter I can get to power the gem of a 120v generator?
Sure you can buy anything. 
How about an AC motor?
Or possible a surplus dc unit to save the conversion.
Better off with 240vac or even 3ph if you run a 15kw generator.
Hybrid would be a better option. 
Plug in your charger to a small generator.
Might not need to trailer it then.