I enclosed the sides of my open trailer yesterday and built a box up front to house my gas cans, blower, and other miscellaneous stuff. I put 2x12 twelve footers down the sides and fastened then on with some 1 1/2 screws and 2 washers right to the steel without having to drill through the steel, just butted them right up next to it and let the washers do the work of holding them in place to the steel and wood. Then up front, I made a box going the width of the trailer, 17 inches back, and 18 inches high using a 2x12 fourteen footer and then since it does not come up over the rail and my gas cans are higher than the 2x12, I put a 2x8 on top of that and enclosed the box with some OSB. Treated wood on everything of course. Got some hinges on the back side to allow the box to open. I put one of those hinges on the front with a thing that turns and locks to keep it shut and got a padlock on that. My dad is going to have a piece of diamond plate cut to fit the top of the box to protect the OSB from weathering. All in all, spent $128 on materials and 2 hours on the labor and it turned out pretty sweet. Only downside now is with the 2x12s running down the sidies, I cant let my gate go down on the inside of the trailer but I have only down that twice anyway and once was yesterday to bring the wood home. If I would have used 1x12s it would allow me to put the gate down inside the trailer but I could not find any treated 1x12 so screw it, I went with the 2x12s. Wish I could take a pic and show it to you guys here but alas I have no scanner. I need to get me one of them!!