I picked up some milsurp ammo cans for 40mm grenades and such- tough as nails, air and watertight, cheap and portable. The larger one I want to build a bracket for to mount it overhead in the rear so I don't lose cargo space, and is long enough to hold an axe and even a pack gun. The smaller one is big enough to pack a compressor, bottle of Slime, tire repair kit, socket set, wrenches, tiedowns, and other recovery gear like snatch block and tree strap with room to spare. I'll get some pictures taken to show what I mean.
They also make great bear-resistant food storage if you're overnighting...