I have yet to meet the perfect overlanding cargo box. Pelican cases are nearly perfect when contents absolutely, positively must be kept dry and dust-free, thus they are the box of choice for, say, photo and video equipment. But Pelican cases are quite heavy for their volume, and pretty expensive for everyday cargo. Zarges (or the similar Alu-Box) aluminum cases are strong, lightweight, and boast excellent interior to exterior volume, but are even more expensive (although you can consider the expense an investment as they last forever with reasonable care).
But more economical alternatives always have some fatal flaw. The affordable Rubbermaid Action Packers are excellent for home storage, but their volumetric efficiency is abysmal and they leak if rained on, so you can’t leave them outside the vehicle when camped unless they’re under cover. If strapped down too tightly (i.e., properly . . .), they collapse. Lower-priced alternatives are even worse.
Several years ago in Tanzania I discovered the plastic ammunition cases used by the South African military, now commercially produced and known widely as Wolf Packs. They’re moderately sized and so easy to arrange in a cargo bay, completely rainproof and reasonably dustproof, and vertical-sided to avoid wasted space (except for hollow corner pieces). They stack securely for convenient storage at home. The Wolf Packs suffer from poorly designed latches—those familiar with them will call that a hilarious understatement— and the lids flex more than I’d like when called upon to do duty as a step, but otherwise they are sturdy, versatile, and sport a certain exotic flair given their origins. Front Runner Vehicle Outfitters is now a U.S. distributor, and for $40 each you can justify several—trust me, you’ll find uses for all you get. We have six, and just glancing around the shop I can see uses for another six. Or ten.
We found that a pair of Wolf Packs stacks and straps down perfectly in the shower grate of the JATAC, under the dinette table. Another rides near the door, and holds all the items we use for pitching camp: drain hose for the galley sink, leveling blocks, guylines and stakes for the awning, etc. I sourced some 1/4-inch thick aluminum diamondplate and fabricated steps for the lids of two of them, attached with small stainless bolts; the three now form a perfect staircase to access the camper when we’re parked.
I also keep two in the back of my FJ40. One holds recovery gear; the other contains a small stove and cook kit, water, and other odds and ends to make an emergency camp or an impromptu picnic.
Front Runner's website is here. They also sell improved steel latches.