How to Build a DIY Reefer Trailer with CoolBot for Commercial Foragers

How Commercial Foragers Can Build Their DIY Reefer Trailer with CoolBot

For commercial mushroom foragers, a reliable cold storage solution is the key to preserving freshness, extending shelf life, and transporting finds safely. But custom-built reefer trailers can cost upward of $10,000—too steep for many small-scale producers. That’s why more foragers are building their own cold storage trailers using an affordable, flexible innovation: the CoolBot.

Here’s how we built our own DIY reefer trailer in rural Idaho for under $2,500, just in time for morel season.

Step 1: Finding the Right Trailer

We started with a solid utility trailer purchased locally from Facebook Marketplace for under $800. It’s a 6’x12′ model with a sturdy axle rated to carry up to 4,000 lbs—perfect for hauling up to 3,000 lbs of delicate wild mushrooms at peak season.

Pro tip: Look for trailers with clean titles, sound axes, and minimal rust. Weight capacity is critical. A flatbed gives you more freedom to frame your own walls.

Step 2: Framing and Exterior Build-Out

Using lightweight metal studs and aluminum sheeting from a local supply yard, we built the outer walls and roof of the trailer. The goal here is creating a sealed chamber, like a walk-in cooler on wheels. For the outer skin we chose thin aluminum panels for weight savings and easy sealing.

Step 3: Insulation is Everything

We lined the inside with 3-4 inches of rigid foam insulation, cutting and gluing each panel in place. Every gap and joint was meticulously filled with spray foam and caulking to eliminate thermal leaks. This step is labor-intensive, but critical—without proper insulation your AC unit will work overtime and still fail to maintain cold temps.

Insulation Tips:

• Use closed-cell foam board for better R-value and moisture resistance.
• Fill every seam, crack, and bolt space—no shortcut here.
• Don’t forget the floor! Cold sinks, so an insulated floor is a must.

Step 4: Cooling with CoolBot

The heart of our system is a residential 10,000 BTU air conditioner paired with a CoolBot controller. The CoolBot overrides the AC unit’s digital thermostat using an Arduino-synced temperature sensor, tricking it into continuously cooling the space down to near-freezing temperatures (if needed).

This system is cost-effective, easy to maintain, and surprisingly powerful for a well-insulated box. In high summer, we easily maintain 34°F even when outside temps hit the 90s.

Install Tips:

• Mount your AC unit high on a wall or into the rear panel to allow even air distribution.
• Drill carefully for the CoolBot sensors and secure all wires to prevent damage in transit.
• Test the system repeatedly before hitting the road to adjust settings.

Step 5: Add the Cold Room Door

To finish the build, we sourced a used walk-in cooler door and mounted it at the rear. This created a perfect airtight seal to keep our hard-earned cold in. Rubber gaskets and metal framing ensure food-safe containment and minimal temperature fluctuation on long hauls.

With weather-tight walls, full insulation, and sealed access, our DIY reefer trailer was road- and forest-ready—at less than a quarter of the cost of commercial builds.

Why It Matters for Foragers and Growers

Mushrooms—wild or cultivated—degrade quickly after harvest. By building your own mobile cold storage, you gain seasonal independence, the ability to hunt longer, and control over your post-harvest quality. Plus, you’re aligning with the values that matter most: sustainability, food waste reduction, and local-first distribution.

Whether you’re storing black trumpets in Appalachia or golden chanterelles in the Pacific Northwest, a CoolBot-powered DIY reefer trailer gives you the flexibility and freshness your customers demand.

Ready to Build Your Own Trailer?

We’re gearing up for a big morel season this spring, and our trailer is already chilling down. If you’re a grower, forager, or food hub looking to build your own mobile cold room, don’t wait. Build before peak season hits and reap the rewards all year long.

Need help sourcing parts or planning your build? Drop us a line—we’re happy to share plans, recommend component suppliers, or answer any questions.

Built by foragers, for foragers. See you in the woods.