I use an aluminum spiral pipe 14" round by 10" long under my 21SE. It has been there since '89 and has never leaked. One end cap is riveted in place and sealed. The other end has a removable end cap with tension locking hasps. It holds my main, two jib sails, one storm jib, my boom, two tillers, parts of a crane used to raise the mast, and my entire rudder system. The trailer also has two aluminum tool boxes full of life jackets and camping gear, a cooler rack for my 94 quart cooler, and a large plastic box full of firewood. The trailer is covered with 18' long by 4'wide of aluminum walk plate which all of this is mounted on.....it takes a V8 to move this beast.....oh, there is a bottle opener on the forward mast caddie......very important.
This is the War Wagon...
On my 16 trailer, I built an aluminum tread plate sail box 10' long... "mail box" style. It is so strong, you can dance on it. One end is welded on and the other end again is like a mail box door. Inside there is a top self for two set of sails and below that is a redwood tray 10" long that holds my rudder assemble and tools. I built this in '85 and it looks maybe a year old...this was the war wagon before the 21...
Aluminum is great, needs no paint, will not rust, somewhat light and no maintenance. Before the winter set in, I offload everything and fill my garage.
Damon Linkous from thebeachcats.com is working on having galvinized coffins style sail boxes built from the company I retired from. Hopefully he will be able to sale these boxes to budget conscious trailer sailors on his website soon.