How I Fit a Roll-Up Tonneau Cover to My M416 Trailer

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10 hours ago

3 min read

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An M416 tub is great for hauling gear, but an open tub fills up with rain, dust and leaves. A tonneau cover fixes that. The catch is that these old tubs are rarely straight, and the rounded rolled edge gives a cover nothing flat to clamp to. Here's how I solved both problems with strut channel and a Ford Ranger roll-up cover.

M416 trailer with a roll-up tonneau cover fitted — The finished cover on my M416.

Watch the build

What you'll need

1-5/8" strut channel (trolley track): two 6 ft (72") lengths for the sides and one 4 ft length for the front, cut to about 45-1/2" so it fits between the side channels. Measure your tub before cutting.
13 stainless steel 1/4" bolts, nuts and body washers: 5 per side and 3 across the front. 5/16" bolts also work.
Exterior caulk: a flexible, UV-resistant, waterproof sealant.
A ratchet strap to pull the tub sides straight.
A roll-up tonneau cover for a 1993–2011 Ford Ranger Flareside/Splash with the 6 ft (73") bed. I used the Perfit Liner (SKU PerfitLinerNR008). It's often out of stock, so check our website at bckrd.com for the latest info on how to purchase the cover.
Tools: a drill and 1/4" bit, wrenches, and a saw or grinder to cut the channel.

Step 1: Take off the tent-rack crossbars

If you have a rooftop-tent rack, remove its crossbars first. The tub sides need to be able to move in the next step.

Rooftop tent on a rack over the M416 tub — My rack and rooftop tent. The crossbars come off so the sides can be pulled in.

Step 2: Pull the sides straight and bolt in the channel

Most M416 tubs are warped, and mine was too. I ran a ratchet strap across the top of the tub to pull the two sides toward each other. Then I bolted a 6 ft strut channel to the inside of each side wall with five 1/4" stainless bolts spaced 12" apart, tightening a little at a time and snugging the strap as I went. The front channel fits between the two side channels and takes three bolts.

The channel's opening faces inward, and its top face sits flush with the original rolled edge. That gives you a flat, straight frame all the way around. On my trailer it measures 72.83" × 49-3/4".

Cross-section diagram of strut channel bolted inside the M416 tub wall — Cross-section: the channel sits flush with the rolled edge, and the cover rail clamps under it.

Top-view diagram of the three strut channels, bolt layout and ratchet strap — Top view: channel lengths, bolt layout and the ratchet strap.

Strut channel bolted along the inside of the M416 tub side — The side channel bolted inside the tub, flush with the rim.

Inside view of the strut channel along the tub wall — Looking along the channel from inside the tub.

Step 3: Seal the gap

Even with the channel bolted tight, the old rounded edge won't line up perfectly. I filled the gap between the rolled edge and the new flat edge with exterior caulk to keep water and dirt from collecting there.

Step 4: Choose the right cover

This is the tricky part. The cover that fits is a soft roll-up made for a 1993–2011 Ford Ranger Flareside/Splash with the 6 ft (73") bed. Measure your frame before you buy. Mine is 72.83" long and 49-3/4" wide, and the 73" cover fits.

Tape measure along the length of the tonneau frame — Measuring the frame length.

Tape measure across the width of the frame at the tailgate — Measuring the frame width.

Close-up of the tape reading 49-3/4 inches — 49-3/4" wide.

It has to be a roll-up or slide cover. A tri-fold folds its panels upward, and on my trailer they hit the tent-rack legs, which lean inward. A tri-fold only works if your rack legs stand upright. A slide cover also works, but it costs more.

Diagram comparing a tri-fold and a roll-up cover under an inward-leaning tent rack — Why a roll-up clears inward-leaning rack legs and a tri-fold doesn't.

Step 5: Clamp the cover on

The cover's side rails clamp to the strut channel the same way they would clamp to a truck bed rail.

Tonneau cover rail clamped to the strut channel at the corner — The cover rail sitting on the channel at the rear corner.

Side view of the M416 with the tonneau cover and tent rack — Cover on, with the rack legs clearing the rolled cover.

You'll need a tailgate

To release the cover, you pull a strap that you can only reach with the tailgate open. My trailer came with a tailgate already fitted, so I didn't build it myself. If yours doesn't have one, adding one comes first. I'll cover how M416 owners usually do that in a separate post.

What I'd do differently

The whole install took me about 4 hours, including working out the plan. Next time I'd look at tent-rack brackets with upright legs. With my inward-leaning legs, rolling the cover back is more awkward than it needs to be.

See you out there. Going nowhere slowly.