Using 70s/80's MDT as camper+4x4 hauler?

Something you may not have considered is parts availability for these older rigs. Case in point- for a short time my dad had an '88 GMC Top Kick 7500 single axle dump truck. It had a CAT 3208, 10 speed Roadranger, air brakes. Really nice driving old truck, it cruised at 65 easily and hauled a 10 ton load without complaint. However, soon after he got it, the throttle started to stick a little, and those who have driven a Roadranger trans know that if the engine speed doesn't drop when you let off the fuel pedal you aren't upshifting-at all. Come to find out the throttle cable needed replaced and there were none to be had anywhere. He had to have one custom made to the tune of $400. In his quest for this simple part he learned that many parts for GM and Ford medium duty trucks simply aren't available any more. So, a seemingly simple repair might end up sidelining your truck and being an expensive or impossible problem.