You have a 6 foot bed (hopefully not a 5) and putting an 8 foot (bed) camper on it?
Good luck.
This kind-of negates couple of the benefits of a TC like being able to tow or taking it off road. Hard to do either with 2 extra feet hanging off the back, TCs already typically have about 20 inches hanging off, so are you going to have 44 inches?
Lot of weight behind the rear axle, so load all weight up to the front.
Your rear tie-down point on camper will be way back there too, so your front one will not be tension balanced, the tie down will pull camper into the front bed rail.
Whatever the seller has for tie down points will not do you much good unless he has the exact same truck. On a normal setup you can get away with good brackets at the front and lesser ones like buttons on the bumper at the rear, but with your 44 inches thing all bets off.
Tork lift makes very good bolt-on brackets for the truck, expenisive, but well worth it unless you are good at steel fabrication and have time.