A well-equipped truck bed makes a big difference in how useful your truck really is. As you add accessories, however, it’s only a matter of time before those upgrades start overlapping. One of the most common conflicts occurs when trying to install a truck-mounted tool box in a bed that already has a drop-in plastic liner.
While drop-in liners offer great protection for your bed, their rugged plastic construction can impede the fitment of other accessories. Thankfully, this is usually resolved with some simple planning and, in some cases, light modification. This guide walks through the general process so you can get a secure, clean install without damaging your truck or your gear.
What to Expect Before You Start
Installing a tool box over a drop-in plastic bed liner isn’t especially difficult, but it does require attention to detail. Most DIYers can handle the job with basic tools, though larger, specialty, or floor-mounted tool boxes may require drilling and minor trimming of the liner. Costs are usually minimal unless additional mounting hardware or accessories are needed.
The exact steps vary by tool box design and truck model, but the fundamentals are always the same: prepare the bed, position the box carefully, follow the manufacturer’s mounting instructions, and make sure everything is properly secured before calling it done.
What You’ll Need
Most installations can be completed with common tools and supplies, many of which you likely already have at home. Always refer to your tool box’s instructions first, but expect to need the following:
Basic tools and supplies:
- Wrenches or sockets required for mounting hardware
- Measuring tape
- Marker (light-colored works best on black liners)
- Cutting tool (razor knife or oscillating tool)
- Sandpaper
May be required depending on the tool box and mounting method:
- Drill and drill bits
- Slightly longer mounting bolts than those included with the tool box
- Rust-preventive paint or primer for drilled holes
- Weather-resistant sealant or gasket material
The ribbed surface of a plastic bed liner can add thickness that affects hardware length, especially for tool boxes that mount through the bed floor. In those cases, longer bolts may be needed.
Preparing the Truck Bed
Before installing anything, clear out the bed completely and clean the bed rails and liner surface. Dirt or debris can interfere with alignment and make it harder to spot fitment issues. Plus, it’s simply easier to work in a clean environment.
Take a moment to inspect how your bed liner is installed, as this will determine how simple or involved your toolbox install will go. For example, many drop-in liners sit under the bed rails, leaving the rail's surface and bottom exposed. If you’re planning to mount a traditional crossover tool box, this makes access for J-hook attachment much easier. Other liners may cover more of the bed or extend into mounting areas. Understanding how your liner fits will help determine whether trimming is required later.
Step-by-Step Installation Overview
Before diving in, it’s worth noting that depending on your bed liner and tool box design, this process may involve making permanent modifications to the liner and, in some cases, the truck bed itself. None of the steps are especially complex, but it’s important to work carefully and avoid rushing through measurements, marking, or drilling.
1. Read the Manufacturer’s Instructions First
Start by reviewing the installation instructions provided with your tool box. While our guide outlines the general process, the manufacturer’s instructions will specify mounting locations, hardware requirements, and whether or not drilling is required. It may even include notes and guidance specifically pertaining to the presence of other bed accessories, like liners.
For added peace of mind, email or call the toolbox manufacturer and ask to speak with a product specialist. These folks often have deep knowledge of the products they sell and can usually answer compatibility questions quickly.
2. Complete Any Required Pre-Assembly
Some tool boxes require light pre-assembly before installation, such as installing lid struts or handles. Completing these steps ahead of time makes positioning and alignment much easier once the box is in the bed. Plus, it ensures you can test out all toolbox functionality before clamping anything down.
3. Position the Tool Box in the Bed
Set the tool box on the bed rails—or in its intended mounting location elsewhere in the bed—without securing it yet. Use a measuring tape to help center the box and confirm that it sits level. Now is also the time to check that the lid opens fully and clears the cab. If the toolbox installs at the other end of the bed, make sure it doesn’t interfere with tailgate operation.
A good fit should feel stable and symmetrical. If the box rocks, sits unevenly, or interferes with other bed components, make the necessary adjustments before moving forward.
4. Mark Mounting Locations
Once you’re satisfied with the position, mark where the mounting hardware will pass through the bed or liner. Always follow the manufacturer’s recommended mounting points. Some trucks include factory holes intended for tool box installation, and many drop-in liners leave these areas accessible. Still, take your time here—accurate marking is critical before drilling or cutting.
5. Trim or Drill (If Necessary)
Not every plastic bed liner requires cutting. For many crossover tool boxes, mounting occurs at the bed rails where the liner may not interfere at all. Other storage solutions, however, such as swing-out tool boxes or floor-mounted units may require trimming or drilling through the liner.
If you’re drilling through the bed, treat it like any other metal surface: drill carefully and coat any exposed metal with rust-preventive paint. If trimming just the liner, take care to cut only what’s needed for clearance and smooth the edges with sandpaper. Always confirm that cutting is actually required before making permanent modifications.
6. Secure the Tool Box
With the mounting points prepared, install the tool box according to the manufacturer’s instructions. Tighten all hardware evenly and securely, but avoid overtightening—especially when clamping against plastic liners or bed rails. If torque specifications are provided, follow them.
Final Checks and Weather Protection
Before loading up the tool box with gear, check that all hardware is secure and that the box sits firmly without movement. Open and close the lid again to confirm smooth operation and proper clearance.
If trimming or drilling created any gaps between the liner and the bed, inspect those areas for potential water intrusion. Depending on the installation, a small amount of weather-resistant sealant or gasket material may help keep moisture out. (This is an area where the bed liner manufacturer will be able to provide more specific guidance.)
Lock It Down With Parts Via
Installing a truck tool box over a plastic bed liner takes a bit of extra planning, but the payoff is secure storage without sacrificing bed protection. Taking a few extra minutes to prep, test fit, and verify mounting details can save time and frustration later.
Buying a tool box online is much easier when you have the right support. Parts Via carries tool boxes from leading brands like WeatherGuard, UWS, Dee Zee and more, and offers guidance to help you choose a setup that fits your truck and your goals. With fast, FREE ship-to-store, you can have your tool box delivered directly to the installer of your choice—simplifying both shipping and installation. Start browsing today and take the guesswork out of buying a truck tool box.