Truck Camper Magazine (online only) had an article about high payload heavy duty trucks having a no camper designation and they went to the factory for an explanation. The factory said once-upon-atime someone ordered a heavy duty truck with both a snow plow package and a camper package and then plowed snow with the camper on the truck and destroyed the front end of the truck under warranty. Since then, if a truck is rated for a service other than a camper which when combined with a camper could cause damage, then the truck gets a no-camper rating. Camper packages are sometimes less than $100 and you get a wire harness and they skip the no-camper letter (maybe add a no plow letter?).