I use two of these: http://go-armynavy.com/military-surplus/field-gear/ammo-cans/us-military-medium-medical-chest-new.htmlDig it. I think you're right about the tonneau though. Maybe newer gens can tweak it to make it work because of the bed tracks. Gives me an excuse to invest in some waterproof bed storage. I sold all my Frontrunner boxes with my Land Cruiser so I get to start from scratch.
and then stack two of these on top: http://go-armynavy.com/military-surplus/field-gear/ammo-cans/us-military-small-medical-chest.html
I had to make some different mounts to hold the tent down to keep the bolts from catching the cases. But these stacked fit PERFECT under the bed bars i have. And two side by side fit perfect between the wheel wells. And they are heavy duty and water tight.
Not sure why they are so pricey now. I bought them for like 50 bucks for the big one each and 30 for the smaller ones each. Im sure with some digging you could find them at that price.
Work nice though. Even with my 5' bed these only take up half the bed and hold a lot. I use one big one for my OSK. The other big one as a kitchen box. Smaller one for additional tools. Smaller one for random things like food. Or sometimes don't use it even.