what length bed?
What about the cap: is it straight or tapered rising?
I added these to both sides and they hold a lot:
Dee Zee Poly Wheel Well Box
Also, I put a 4 or 5' wide shelf across the truck bed, located as close to the cabin as possible.
Be sure to put a tall "lip" on the shelf so that things don't slide off. On this shelf I store camp chairs, propane stove, stove stand, child's sled with firewood. In fall, everything gets replaced wth goose shell decoys.
Fishing rod holders are attached to the cap's ceiling -- out of the way and bungee corded so that they don't bounce/slide out.
Finally, I installed a 4' length of steel "L" bracket, bought at Lowe's.
I made a bunch of "S" hooks to hang my ball caps, flashlights, hand clippers, etc. This was the smartest move b/c I also attached battery powered lights so the interior is now lit.