We had our original SB camper for 17 years. It sat on 4 different trucks (all Ram diesels because I retired from Cummins). One of the trucks was a longbed, all I did was make a rectangular frame out of 2x8's or 2x10s, can't remember which, it's still sitting in my shed attic. Strength isn't an issue, you need to decide how high your bumpers on the front of you camper are when you back your truck under the camper. You want the framework tall enough that the bumpers hit the framework, not above the framework. If you make the framework too short (2x4s for example), the bumpers will be above the framework if you're not careful, and when you lower the camper into the bed of the truck, the bumpers will be torn off.
