I've decided that a carhauler is only handy a few times a year, so I built some 26" sides that I can bolt on for a 15x7 trailer
I used 1.5" x .250" angle and 3/4" pressure treated plywood. Mounting those 15' sides is a 2-man job. I may cut them at the center post and make 6 removable parts instead.
I'll have to load carefully, as the load will be biased to the front. Maybe later I'll make the tail part of the cargo area.
Rear gate has a hinge on both sides to open either side, or remove the gate. I'll be using a trailer clip to retain the hinge pin in place.