My friend listed his GMC on AdvRider. Truck is clean and well maintained. I know that he will sell it without the utility bed at a lower price... which made me think it could be a good start to a 4x4 camper build.
FOR SALE $19,950
2006 GMC 3500 4x4 Duramax, Allison tranny. Extended cab. Dually. 130 000 miles. Enclosed contractor's bed. Tow package. San Diego. Can be sold as a cab and chassis.