Custom Underbody Toolbox Mount for Flatbed Truck – Built to Last

This project was a straightforward goal: mount a Buyers underbody toolbox under a flatbed truck — but build it in a way that actually holds up to real work.

A lot of toolbox installs rely on thin brackets or light mounting points. That might be fine for light-duty use, but on a work truck that sees rough roads, heavy tools, and daily use, those setups don’t last.

So instead of a quick bolt-on install, we built a custom heavy-duty mounting system.

The Setup

This install used a steel Buyers Products underbody toolbox mounted to a flatbed work truck.

Instead of hanging the box directly from the bed, we fabricated custom angle iron mounts that:

• Weld directly to the underside of the flatbed

• Provide a wide, stable mounting surface

• Support the toolbox evenly across the top

The toolbox is then bolted to the mounts using:

• 3/8” Grade 8 bolts

• Nylon lock nuts (nylocks) to prevent loosening

• Washers for proper load distribution

Fabrication Process

The mounts were built from steel angle and welded into rigid supports designed for long-term durability.

Key details:

• Fully welded ends for strength

• Tight, clean fitment to the toolbox

• Designed to spread load instead of concentrating it on small نقاط

Once fabricated, the mounts were:

1. Positioned under the flatbed

2. Welded directly to the bed structure

3. Aligned for proper bolt placement

Final Installation

With the mounts welded in place, the toolbox was bolted up from underneath.

This creates a system that is:

• Structurally supported by welded steel mounts

• Mechanically secured with high-strength hardware

There’s no reliance on thin sheet metal and no movement once installed.

Why This Setup Works

Strength

The load is carried through solid steel mounts, not just bolts or thin material.

Vibration Resistance

Using nylock nuts helps prevent hardware from loosening over time — a common issue on work trucks.

Long-Term Durability

Spreading the load across the mounts reduces:

• Hole elongation

• Metal fatigue

• Cracking over time

Serviceability

Even though the mounts are welded, the toolbox itself is still bolted on — so it can be removed if needed.

Built for Real Work

This setup is designed for:

• Work trucks

• Construction use

• Daily tool storage

• Rough roads and job sites

It’s built to handle:

• Chains

• Tools

• Hardware

• Heavy daily use

Need Custom Fabrication Work?

If you’re looking for:

• Underbody toolbox installs

• Trailer modifications

• Flatbed modifications

• Custom welding and fabrication

We build setups that are made to last — not just look good.

Serving Corbin, London, Williamsburg, Richmond KY and surrounding areas.