Flip Pac or Custom
If I had the cash, I'd go flip-pac. Since I am on a budget, I built my own platform with a flip-open lid and an extension for sleeping and bought a truck tent to go over it. The platform I designed is securely lockable (it locks the tailgate too). I built it for $250 and paid another $250 for the truck tent with a good rainfly. It survived hurricaine season in Mexico for 3 months in '05, and I saved a ton of cash over any other option we could find.
With a lockable platform, queen-sized self-inflating airbed with foam inside, and a good rainfly that was all the wife and I needed to enjoy a fabulous expedition that took us through Mex from coast to coast, as far south as you can go in Oaxaca and back home to AZ.
Downside = its a little ugly. Every other side is up, or so we decided.
I have a more detailed build thread on TTORA at:
But here's a shot of it with the lid closed.
If you can handle the fact that it's not all shiny and pretty, this could be an option for you.
'03 D-cab Prerunner (4wd conversion), 3.4 L V6 Auto TRD, Rear E-locker w/ Guard, Front ARB Air locker, 4.88 Gears, BFG MT KM2 255 85R 16, BudBuilt Front IFS & Belly Plate Skids, Trac Bar, Custom Tank Skid, Demello Sliders & Rear Tube Bumper, CBI Frame Plates & Custom Front Tube Bumper, Aisin Man Hubs, IVD c/o's, 3" All Pro Leaf Packs, 1" Toytec Shackles, 12" Billie 7100 SB's, F&R Timbrens, 1.5" Wheel Adapters, Diff Drop, BPV Bracket, Pinch Weld Mod, No Swaybar, K&N, etc.