I'm trying to keep the weight down because I have to ship this thing but I am going to put a picture frame style (open center) brace in the middle from the back of the box toward the port. This will brace the top and back to the bottom. It shouldn't need more than that because the port braces the front and top to the bottom. I suppose I could add bracing to the sides from top to bottom but I don't think they'll need it. What do you think?
I would at least do some strap bracing on the side panels as they're pretty big and will easily flex. Shipping is going to cost a decent amount, hope you figured that into the price...