So, because I already had a stack of 2x6's, I thought I'd save some cash by ripping some and biscuit joining two together with some Gorilla glue. I thought I'd reach a wall height of 9". I decided on 9" because the spare I'm planning on mounting will be 9" thick laying on it's side. I'm building with the idea that I'll be upgrading to 26x9x12's in the near future so I based my measurements around that. As stated before the tire will be mounted flat. After glueing and clamping the walls overnight, I then ran them all through the planer to reduce thickness down to 1.25 " and to give them a uniform look. I realize I'm putting a fair amount of weight back there but, I need it to be stout. Plus large enough to haul extra gear especially if I can make it to the Magruder Corridor ride in Idaho. I'm also concerned about having much more weight back there working against the P5 when ascending steep rocky climbs. I don't need anything pulling me backwards. I may also taper the side walls down and even lower on the rear wall, to reduce weight, but wanted to start with more 1st... We will see how well it holds up at the Takeover. I'm installing 1" spacers and the offset rims which will put me out at 54". Hopefully that will make it stable enough.....I had to leave space between the ROPS and tool box so I could still open the lid but, also managed to create a perfect space to store my MaxxTrax. Tomorrow I'll finish glueing and screwing and then give it a few coats of OD Green exterior oil based paint. After it dries I'll mount it onto the rack and also attach the tool box. All in all, I can still see over it better than when I had the taller toolbox installed.. I had also considered making a hinged rear tailgate, but thought that might make it weaker. Especially if we flop to one side.
Side note; I had also made the base for the tool box the same way did for the side walls. I had needed to raise it enough so that the spare tire would fit under the overhanging lip of the tool box.
Side note; I also left enough space maybe 1/4" between the bottom plywood and the ROPS to allow for movement of the rear panel.