For the sizes needed for a rig your size, 13,500 or 15,000 btu, which in either case will need 3000 to 3200 watts on a genny.
Now for the fun part, find the one you want.
Inverter units will run basically from a
Predator from Harbor Freight, 3500 watts $700
Champion w or w/o remote start 3000-3200 $750 - $900
Honda and Yam 2800 - 3500 $1800-$2000