Carefully trim away the unnecessary fabric and straps, sealing any frayed ends with a torch or lighter. Remove the side frames. For the forward post, measure the angle with a bevel gauge and cut using a jig saw or angle grinder. I used a tubing cutter for all of the perpendicular cuts. Planning on hauling groceries, I made the new height about 14" so I wouldn't crush the bread.
The sides are made of 3/4" tubing. I tried to reshape these but they kinked too easily. I made new top bars for the side panels using 3/4" aluminum plywood edging. An 8' length was about $8 at the local Home Lowespot. The tubing fits snugly inside, and I secured them with rivets.You'll want to grind or file down the sharp edges before riveting the top bars in place. I cut the forward channel at the same angle as the tube, and hammered the tips flush with the tube to reduce snags.
I relocated the top crossbar to the back and had to shorten it by about 1 1/2". This really helps it hold shape, keeps things in, and retains the folding capability.
The trailer came with a screen cover. I added snaps to the bottom of the rear corners and now have a little something to keep my stuff in. I also added some webbing side straps using snaps. I may modify the screen cover, or make a new one, that's waterproof and/or opaque. Sooner or later the bottom fabric is going to go out, and then I'll probably replace it with an aluminum sheet.
It's also a simple matter to make the trailer several inches narrower, which would probably be better for trekking. The secret is where the hitch attaches to the trailer. You can flip this and trim twice the difference from the middle, around 6 inches. It'll mean making a new bottom and splicing the cuts with dowels or more aluminum tubing.