I wasn’t able to find the 4″ except in bulk packs on the www. I got the 2″ Foamular which said 25 pounds per square inch non-compressibility. This seemed to have reduced the cabover and roof contact by like 95% on some rough roads and sensible driving! Still I’d prefer for this not to happen at all.
The foam insulation did compress so now there’s a “track” on each side of the foam and that means the TC was lowered almost an inch! I’m wondering if adding a second 2″ will be of any help at this point. The foam also cracked in a couple of spots.
All in all thought the solution worked quite well and of course provided extra insulation.
I also made some angle brackets for the front which A)helped loading tremendously and along with the insulation seemed to have stopped the sideways movement (whereas a bed mat didn’t do that at all) which was great because the Northstar on the 2017 F250 is a very tight fit when it comes to the tie downs being close to the truck.