I've just been making some modifications to a utility trailer that I'll tow behind my truck/camper on trips where I want to take along some toys. Part of that was the addition of a pair of storage boxes and support structure to mount either a pair of kayak cradles or crossbars. I can attach or remove the mounts and boxes in about 30 minutes. The angled tubes at the top of the uprights will support a kayak cradle on each side or can be replaced with other parts that will support crossbars across the trailer. I'll have a motorcycle in the center sometimes, hence putting the kayaks on the sides. Photo is of a test fit prior to painting.
Relevant to this thread, I was faced with the task of removing mill scale and some rust from the steel I used. I first thought about grinding it off, but I'm not really into tedious work like that and I don't have a helper to pawn it off on, so I looked into pickling.
I've ended up using a 25-30% muriatic acid bath and it works great. About 30-45 minutes in the bath, rinse thoroughly and I rub with rough side of a ScotchBrite sponge...easy. Small pieces I put in a 24" x 16" x 6" plastic storage tray, but that didn't work for the main uprights that are 40"...what do do.
Bingo...4" dia foam core PVC pipe with a section cut out of it to about 3" from each end, then end caps installed. This photo doesn't show that the section cut doesn't go clear to the end. I only made it 4' long, but could have made it the full 10' length of the pipe to accommodate longer pieces. The end caps are not glued on, but they fit tight enough to not leak. The end caps were more than the pipe, so I figured I'd like the option of re-using them if I ever need a longer setup. When using this, I clamp it in an old B&D ShopMate. I can get two pieces of 1 1/4 square tube in it, which wasn't really a problem on this project, but I'd probably have made it out of 6" or 8" if doing a trailer build. Obviously, you could use a coupling(s) and make a 20' version, if needed.
Cheers!