Re: Alum. flatbed input.

Have seen several that have done it. Most have boxes on the bed surrounding the camper. I see no reason you could not do both above and below. But you should ask yourself, how much stuff do I really need to deag along with me?
As for the truck? Consider a 4500 or maybe a 5500 if your going to a large camper.
You might also look at Host campers. They have some really interesting floor plans.