Good thinkin', here's how you do it. Use 2X10's or 2X12's (depending on how tall your wheel wells are inside your bed. Run them the full length of the bed and across the front, you can attach them to each other with L-brackets so you can remove them as one unit (I don't suggest affixing them to the actual bed of the truck.) Cut a platform to put across the top out of 3/4" plywood or equivelent, this will be your bed. You can either screw it down to the 2X10's or not depending on your storage requirements when you remove it from the truck. If you want to get fancy, you can screw small hydraulic lifts (like those on the lid of your shell,) to the 2X's and the platform so it will raise up for easy access. Now, since you don't have a 2X in the back, you can build a drawer that will slide in and out, our build a door to access the storage underneath. The advantage of the drawer is that your gear won't all slide to the front while traveling, and you will be able to organize better. However, it all depends on your budget. If you want to do it on the cheap, use a 2X10 in the back that can be removed (use L-brackets screwed into the side boards that will "sandwich" the tail board, you can then slide it up and out.) You can then slide out the top platform to access your stuff, or just wedge something in to hold it up while you get your gear out. You can get as creative as you want by either building the slide-out drawer, building adjustable compartments inside, run another 2X10 down the center so you have two top platforms that are easier to manage (and hence, two storage compartments,) etc, etc. I also recommend building small corner shelves in the front corners where the shell meets the top of the bed for your flashlight, water, etc. You can build the whole thing so that it pops out in moments and stores fairly flat, and without making any permenant modifications to the truck or shell. Hope this helps, if you need any more help, simply ask. Paddle hard, paddle safe.