It will be an extremely rare camper that will allow you to slide it forward in the bed and leave some bed "hanging out" behind the camper. Maybe you can find on. I'm not sure how you'll make the rear tie downs work out. You would have to get something custom built. You might just consider getting a side entry camper. That's what I have. I really like it because I often have a bicycle rack on the back or I'm pulling my boat or something. Having my camper door on the rear would be a pain.
I know you want to carry come heavy dirt bikes on a rear carrier. This does present a problem since the only way to have a side entry TC is to get one that hangs back past the end of the bed about 2 feet. This means you need an 11' camper for a long bed or an 8' camper for a short bed.
The Lance 830 would work great on a short bed. You would need a Torklift Super Truss and Super Hitch to haul the dirt bikes.
