A short bus will handle more weight and tow more...
Diesel will last longer and get better mileage, plus pulls harder... I have an off road 4x4 that I tow to the trails... I've pulled it with several different truck and diesel is the only way to go...
My bus is 25' with 20' of living space with a diesel and an allison tranny... I haven't used it to tow yet, but I have a buddy that has an International 5 yard dump truck and the frame, running gear, engine and tranny are the same as what's in my bus... Basically my bus is a dump truck with a bus body...
And yep, they also look cute...