I used to have a 36'gasoline motor home on a F-53 Ford chassis. I think anything longer then 36' would be too long and you would get too much wag the tail on cross winds. Also my 36' would drag the rear end on just about any dip. Later I found out it had air bags and I added 90 lbs of air which really help lift the rear end up and it seemed to help stabilize the motor home and it gave more carry capacity.