Trunk structure
The goal of this project is to equip the bed of my L200 with a rigid, flat, and square base frame, watertight to the edges of the original structure. This protects the original bed while providing a solid foundation for securing equipment or mounting additional structural modules.
The design was created using OpenSCAD, with a focus on standardized materials such as steel tubes and metal sheets.
Here is an interactive 3D model of the designed structure. You can left-click to adjust the viewing angle, right-click to pan, and scroll to zoom.
Base frame
The first step of the manufacturing process was to determine the optimal cutting distribution in order to minimize steel waste. The raw steel was then purchased from a local supplier, after which each bar was cut to the dimensions defined in the simulation.
Next, the side rails were tack welded to their mounting brackets. These brackets are installed underneath and later used to clamp the frame against the original bed sheet metal:
This approach improves overall rigidity while also helping with sealing and watertightness. Along with the clamping mechanism used to secure the frame to the bed, an additional hole is drilled in the side of the beam to align with an existing bolt on the bed.
With the brackets tied to the square beams, it was then possible to drill general-purpose holes for securing equipment, attaching ropes, or mounting modular elements:
Base frame assembly
Before welding the side rails to the third cross member, a full fit check was carried out to ensure proper alignment and prevent issues during final assembly. This test also accounted for the estimated additional thickness resulting from the zinc coating.
Once all checks had been successfully completed, the tack-welded beams were reinforced with full weld beads.
The assembly was then welded to the remaining beams to form a square U-shaped structure designed to slide into the existing bed frame.
Removable upper frame
With the new steel base completed, it was time to move on to the accessories, starting with a common upgrade for pickup beds: a bed rack. In this case, cylindrical tubing was chosen to improve resistance to forces from different directions, while also maintaining a clean aesthetic. However, this required testing a fishmouth cut at the end of each tube for proper welding fit. The cuts were then shaped using a thin cutting disc, and each joint was checked for squareness before welding.
With the side pillars ready, the next step was to weld them onto the mounting plates (steel brackets) bolted to the top of the steel base. To accurately position the tubes before tack welding, I used photography magic arms as temporary supports.
Before welding the upper tubes to the pillars, the tubes were fitted with small sleeve connectors at their front ends. This design allows the structure to be easily disassembled and stored in a standard flat basement.
Unfortunately, the internal dimensions of the connectors did not match standard tube diameters, so I machined custom internal sleeves from a 40 mm steel rod using a lathe.
In addition, I prepared internal disks, which were drilled and fitted with centrally welded nuts to allow bolting. These components were then welded into the sleeves.
These connectors were then welded to the main tubes:
With the pillars ready and bolted to the frame, the upper tubes were placed on top, aligned, and welded:
To prevent the transversal tube from rotating, small notches were added to the design.
Installation
With the full structure complete, it was installed one last time before undergoing galvanic protection.
Surprisingly, the default width without constraints is identical at the front and rear, and the vertical clearance aligns perfectly with the pickup’s roof height (c.f. the long bar on the 3rd picture).
Small “stress” test for the structure:
N.B. The front nuts were not installed for this test.
The front internal nuts are barely accessible, so I designed a a small 3D-printed cage to hold them in position inside the tube. However, the part was not yet printed at the time, so the test was carried out without all front bolts in place.
Current status
The structure is now undergoing galvanic protection before painting.
Next ideas?
To be continued…