Here's how I converted our trailer into a cargo hauler worthy of a long trip.
Step 1: Teardown
Start by removing all of the nylon canvas bits that you can. Everything on our trailer was held on with nylon webbing, plastic cinches, and plastic buckles. There are also three metal supports which thread through loops on the canvas sides and back which must be removed.
Ours was designed to fold down so it would fit in the trunk of the car. I think we did this once. Anyway, after removing the roof, there are two large knobs which hold the side supports to the rear support (second photo). Once these are removed, the bolts at the front (photo three) and the back (photo four) should be removed. Once the supports are disconnected from the main frame, the remaining canvas should fall off. If it doesn't, go back and look for velcro loops or straps which you missed.
Step 2: Moving the Foot Bar
The foot bar is held on by a couple of bolts going through a clamp (photo one). This trailer requires a small allen wrench and a metric socket to remove these bolts.
The tricky part is the left (driver's?) side. The towing bar attaches on the left side (photo two), complicating the removal of the foot bar. This one needed the bolts completely removed and the clamp spread so it could slide off of the main frame. The other option would be to remove the two bolts holding on the rear of the tow bar and then slide the foot bar clamp down the main frame. The only problem with this plan is the foot bar clamps don't slide well on the main frame - I tried it on the right side.
Now is also a good time to take off the wheels so you don't have to fight the spokes with the allen wrench (photo three). On this trailer, the wheel is held on with a pin which is kept in place with a clip. To get the wheel off, the clip is flipped, the pin is removed, and the wheel falls off.
I relocated the clamps to the front of the frame doubler and tightened the bolts (photo four). If you had to spread the clamp on the left side, it may take some effort to bend it back into shape so the holes align. I put the wheel back on to make sure nothing interfered with the spokes, but it also made it easier to move the trailer around while I built the deck (photo five).
Step 3: Installing the Deck
Holding everything together are short wood screws countersunk into the cross bars. I did leave gaps between the boards to let water through (you can see them in the shadow in photo one), but keep in mind that it means the whole deck can shift out of square. This really isn't much of a problem since I placed the cross bars so they would butt up against the main frame (photos two and three). A close look at photo three reveals one little challenge: the rear of the frame is formed with two curves instead of square joints between different lengths of pipe. The edges of the cross bar were filed and sanded to fit snugly within the curves.
The first version of the deck was held on with zip ties, but this version is a bit more sophisticated. Four 90-degree angles were screwed into the cross bars, then persuaded over the main frame with a hammer (photos four through seven). This means it will take a screwdriver to take the deck off, but I don't anticipate doing that very often.
Step 4: Trailer Complete!
I know I left several details out, but each trailer is unique and will require a different solution. You may be wondering about the yellow rope. That was wrapped around there to take up the slack between the tow bar and the mount. I was tired of it rattling around....
The trailer came with a hitch which was a big clamp for the left-side chainstay. I replaced it after the hitch came loose one day and destroyed my favorite frame (I am thankful that the kids weren't in it at the time). The new hitch is an adaptation of the Bike Friday quick-release hitch (see their website for details).
For tying things down, I looped some small rope around the crossbars and main frame between the deck boards (another reason for leaving a gap!). To these loops, I either tied a rope directly or attached a carabiner. Be sure not to use those silly keychain carabiners! I may put some eye screws into the frame or directly into the deck if the ropes ever fail, but I like having the extra security of the ropes.
Another option is to replace the deck with a storage bin. In that case, the crossbar would support the middle of the bin, but there would be issues of ground clearance at the front and back. I've been measuring different bins, but I haven't found quite the right dimensions. Perhaps I will need to take up vacuum forming....
Good luck with your own trailer conversion!