The idea of using the rafters in the garage is a great idea. Unfortunately it won't work and here's why.
I don't have a garage, I have a dedicated two-car sized shop - no way to move the stuff around enough to get a vehicle inside. And besides that, my truck is a dually and is eight feet wide at the wheel wells. Unless I had a two-bay sized door I couldn't get it into a normal single car sized door. And add to that the fact that the truck is over seven feet tall (to the "clearance" lights) and it really won't fit into most standard garages. So I have to find an external way to get it off.
As to what a cap is verses a camper shell, the first pic is a side view of my truck with the cap installed. The second is what I think of when someone mentions a camper for a pickup truck:
truck-side.jpg
Truck Camper.jpg
Now, why do I have one...well, there are times when I need to have the contents of the bed secure and dry (like when I'm moving my family every 2-3 years). It stays off a lot, but that means it gets stored on the utility trailer which I would prefer not to tie up like that. Even if I do store it on the trailer, I still have all that effort of getting it on and off. And no, my truck is not hospital clean - it's a truck with all the dirt, grime, and scratches that comes with utility work.
As for not taking it off at all, I like the idea and often use my utility trailer, but there are times when the truck bed works much better. In the past I loaded 10,000 pounds of concrete into the bed without a problem. My trailer wouldn't have handled that load. And the recent use was for picking up 4 yards of mulch in one shot, which I could easily do with the bed and some side extensions. The trailer would have required a lot of effort at building sides for it (it's a 30 foot flat-bed car hauler). I also have one of the bed unloader roller things which work great at getting stuff like mulch, dirt, and stones out of the bed easily.
Any more ideas would be greatly appreciated.
Be well,
Doc