Not too many people would dado the dividers like that... most just cheap out & butt them together, caulk & screw 'em together.
You have some woodworking skills.
I didn't even get a jack with my truck
If you don't want to keep it in the cab, taking up room, just grab a plastic rubbermaid type storage box (with locking lid) & stash it in the bed. If you're worried about rusting, just shoot it with some rustoleum before you stash it in there.