I’d say not may have the “exact answer”.
1.5” seems a bit light, but may work. Probably fine under normal conditions but hitting a big dip or frost heave at highway speeds might test that theory. I’d shoot for a bit more. Nothing a sheet of plywood or 1” foam under the bed mat won’t cure.
congrats on the new rig!
It seems like if it did slightly contact at the center of the cab roof that it wouldn't cause any permanent damage but would give me a warning that I need to do something about it. It also depends on how the cab and camper move in relation to each other. I.e., if it was a straight pivot at the cab to bed interface then 1 1/2" at the center of the cab would equate to about 3" required at the windshield. I need to figure out if I can modify the shark fin antenna but keep it on the cab roof or completely move it somewhere else.
I agree with your assessment would feel better with at least 2" of clearance. Another thing that might help if they are still available was shock absorbers between the camper and the truck. I think Lance had these. On mine I use a half inch plywood which has 1/4 inch dense carpet attached to it.
