If you have an older AK and a newer truck, you may need to raise up the AK a bit to clear the walls of the bed so the camper will set on the truck bed and NOT on the truck bed sidewalls...to do that you can't just toss in a couple 2 x 4s crosswise. The proper method should be to make a BOX out of 2 x 6s so the side walls, front and rear panels are resting on them and not just the floor panel...then add several cross members to support the floor and add inuslation in the voids. Paint them all beforehand with an oil based primer and finish coat to keep them from rotting and wicking moisture up to the plywood.
Do it once, do it right.