There is a lot more movement up there than many realize with truck frame flex and cab over bounce. I'd want at least 3" clearance, which would be easy for you to do with a flat frame built with 2x4 or 2x6 lumber or a sheet of pink/blue insulation board for support
I've sen 3" mentioned before. I've also seen some comments that some Fords had more frame flex than other trucks. My current truck (2000 K3500 crew cab long bed) has 2 1/8" between the center of the cab and the bottom of the camper overhang and hasn't hit in 20 years. But I only use a 1/4" thick rubber mat in the bed which minimizes the amount of camper bounce.
Truck manufacturers brag about how strong their frames are on new trucks, I just wonder if that translates into less flex between the bed and cab. I'd prefer to keep my center of gravity as low as possible and minimize the amount I have to raise the camper.
GM pickups have much less flex than a Ford, you can search frame flex videos and see the drastic difference. A standard rubber bed mat will also provide cushioning while helping hold the camper firm, the problem lies in many go cheap and heavy by using horse stall mats that are three times thicker and offer plenty of rocking potential. My setup is a standard rubber bed mat and an aluminum superstructure camper with minimal movement up top, but it still does move some.
I really wanted to make a GM truck work since they will let you get a gas engine in any trim line. The problem I ran into was the 2024 Truck-Camper Loading guide was completely wrong for the cab height. It showed the cab height as 40.8" but I just happened to measure the cab height when I was taking some other measurements and it turned out to be 44" and that didn't include the shark fin antenna. I'm glad I found out before it was sitting in my driveway although I could have dealt with it. The ram is 42.5" which was enough to sway me that direction (among some other things). Ford was higher than I even wanted to consider.
I'm hoping to be able to trim my current K3500 bed mat to fit the Ram. I'm also hoping that the Ram frame flex is low enough to let me get away without building a platform.
I have about 4, i could get away with and feel comfterable with 3.
frame flex doesn't mean it is weak, a fram that will flex in most cases will usaly be stronger to a point as it is able to adsorbe slight movment where as a ridgid fram can't and will be work stressed and eventual fail. now we will probably never see thins in our picks ups but just wanted to put that out there.
the major issue you are going to see is if the brand crowns the bed for weight handling, this will let the camper rock back and forth more which lets the cabover get closer and farther away from the cab roof when hitting bumps and even accelerating and braking. some people have made up for this by shimming a bed suport up to make a flat surface for the camper to sit on but then your defeating the purpose of the crown, so I am not sure what the answer is in this case, maybe some one with a crowned truck can chime in on this one, but it is a good idea to get a knowen strait edge the length of you bod and see if the bed is crowned or not then you know.
As far as I know the crowned bed is limited to GM trucks but I'll verify the Ram bed isn't crowned with a straight edge.
