Every other tool box takes space out of the bed. These two do not, because they hang underneath it. That is the whole argument for them, and it comes with a set of tradeoffs worth understanding before you drill anything.
What Is the Difference?
An underbed box mounts beneath the bed of a pickup or the deck of a flatbed, hanging in the space between the frame rail and the outer body line. An underbody box bolts directly to the frame of a flatbed, service body or chassis cab, usually as part of a run of compartments along the side.
They Free the Whole Bed
This is the reason to fit one. The bed floor stays completely clear, the rails stay clear for a rack or a cover and there is nothing to lift over when loading from the side. On a truck that carries material every day, that is worth more than the convenience of a box you can reach without bending.
Capacity is respectable too. Underbed boxes are commonly offered from around 5 cubic feet up to 20 cubic feet in the longer jumbo sizes, which is comparable with a full-size crossover.
Clearance and Ground Exposure
A box hanging below the bed reduces the clear space under the truck, which matters on ramps, kerbs and rough sites. Check the departure and breakover clearance with the box fitted rather than assuming the frame rail is the lowest point.
- Measure the drop below the bed line before ordering a deep box.
- Check clearance to the exhaust, the fuel tank and the spare tire carrier.
- Watch the rear wheel travel, since a box near the arch can be caught by a tire.
- Confirm the door swings clear of the tire at full lock on a dually.
Expect to Drill
Unlike a crossover box, these bolt to structure. Underbody boxes bolt to the frame or to purpose-made mounting brackets, and underbed boxes usually need holes through the bed support or a bracket kit sized for the truck.
Use the bracket kit intended for the box rather than improvising, and treat every drilled hole with primer before the fastener goes in. A raw hole in a frame or a bed support in a salt state will be rusting within a season.
Weather and Access
These boxes live in the dirtiest part of the truck, taking spray from the rear wheels. Seals matter more here than on a box sitting in the bed, and so does the drain arrangement. Check the seals and drains each spring.
Access is from the side, at knee height, which is comfortable for most items and awkward for anything heavy. Compare underbed tool boxes against underbody tool boxes, or see the full tool box range.