I have a mid-rise cap on a 6' bed, and I followed this advice:
http://www.highinfatuation.com/blog/dirtbagging-101/
and built a dead-simple half-platform at bed rail height. Just 2x10s covered in cheap grey carpet from the hardware store, staple-gunned in place. Stapled big patches of hook-side velcro to the underside, and they stick on the carpet lining on the cap rails. About 2.5' of platform space, with plastic crates stacked on top and lashed in place with rafting camstraps. All my thermarest mattresses kept permanently in the bed, with a 4" foam mattress on top, cut to size and covered with a few old fitted bottom sheets. Feet go under the platform to sleep. Plenty of room to sit up inside - two people can cook and maneuver when closed up, three people can take shelter from mosquitoes and rain in a pinch. I never liked the cramped, coffin-like space of a bajataco style full length platform; this is a lot more flexible and comfortable to hang out in. I've spent many, many nights with a laptop on the shelf, watching movies.
Not the best illustration, but here you go: