I ran into the need for quite a bit of additional height for my Bigfoot 2500 camper on my 99 F350. When I purchased the camper I drove to San Luis Obispo to check out the Craigslist deal and arrived about 9pm ready purchase. After a quick look, I bought the camper and proceeded to try to get it loaded on my truck. When we finally had everything aligned and began to lower the camper it became clear there was not enough overhead clearance. It ended up being short by almost 3"! Thankfully, I had eight 1" thick 2'x2' foam squares I used with my old camper to give it 1" of additional lift. Of course the eight foam blocks left me about sixteen blocks short for the height I needed with the new camper so what I ended up doing was stacking three layers of foam in the front of the bed and one layer in the back. This caused the camper to sit at a raised angle enough to clear the cab and though quite awkward, was enough to get me home.
Later on I purchased the additional 16 blocks I needed to raise the camper evenly. The current setup includes:
1. Rubber bed mat cut for the F350 bed sits between the metal bed and the square foam.
2. 24 1" thick 2'x2' foam squares arranged 2 across and 4 long in the bed. They are stacked three high and glued together to form 8 3" thick 2'x2' squares.
3. Rubber bed mat cut for flatbed trucks but sits between the square foam and the bottom of the camper.
This solution gives me the clearance I need and helps to prevent the camper sliding around in the bed of the pickup. The great thing it is if I need to use my pickup bed, I unload the camper and then take the 3" thick 2'x2' squares and throw them inside the camper. They are light weight and small enough to not be a hassle when storing. The rubber mats of course stay in the bed of the truck.
For those wondering, the rubber bed mats I got from Tractor Supply and the Pink 1" thick 2'x2' foam squares I got from Home Depot in the insulation aisle. I think it was labeled "project tiles" or something.