My church had a 6'x12' cargo trailer and we wanted to use it on mission trips. The main focus was to add shelving but keep the floor clear so we can haul material or personal items of the participants. They charged me with installing some kind of shelving or organizational cabinetry. Everyone kind of wanted to use pre-fabed shelving from one of the big box stores. Instead I designed some overhead and upright shelving, this is an original design created by me. I wanted to maximize space and make it safe, if you create to much of a top load on your trailer you can make it top heavy and it will sway or topple over the trailer when going down the highway. I started by measuring out the inside of the trailer and sketching up some rough drafts of the design. I also decided to put doors with hardware cloth (Squirrel Cloth) that way the tools would not come out going down the road. Also I decided to put some bulk tool storage in the front nose of the trailer, rakes, shovels, pick axe, sledge hammer, etc.
I started with the upright shelves first, make sure to place these over the axles of the trailer it will help distribute the weight more evenly. Then you place the horizontal shelving across the top of the upright and tie the two together. Then you screw the two units to the wall, I used self tapping metal screws and tied into the wall supports of the trailer. This makes the shelves very strong, I weight 200 pounds and can hang off of the front. 3/4" cdx plywood was used for all shelving, it is strong, cheap enough, and if it needs to be reworked in the future anyone can work on it. Also I used 1x4's for the doors and face trim, it makes the doors light and strong enough to stand up to years of use. I used pocket hole screws and kregs pocket hole master jig to make all the shelves and doors. I believe this is a stronger joint than a dado because you don' t dado out your wood. The doors were made out of 1x4" material cut down to size, I then added hardware cloth so you could see the tools stored away but it would also keep the tools in the shelves. Also added small wooden knobs from the hardware store as handles.
Materials list:( will depend on size of trailer)
6 - 3/4" cdx plywood
12 - 1x4x8 white pine
2 - rolls hardware cloth
9 - 2" hinge pairs
12 - wood knobs
12 - sliding bolts ( to keep doors and drawers shut while traveling down the road)
3 - rubbermaid organizer strips and accessories