I have a 7 x 16 open trailer that I want to put 4' sides on. I would prefer wooden sides out of plywood. The thing I am trying to figure out is how to design the back so that it won't "flap" around going down the road. The front of course can be all tied in together but the back has to stay open. I know my truck sides after a while get really "floppy" and I keep having to shim them up and then they start to look all trashy because they are not inline with the truck. I may have just answered my question in my mind. I guess I could use some angle iron on the back corners but bolt it together instead of welding it so it can be removed. Any other ideas?