bracing a box will keep it more rigid which means less energy is being used to flex the box, and more energy is being used for output. You can do it multiple ways, I use wooden doweling but you can use threaded rod or some people even take a piece of MDF and use that to brace it all. It's just something to connect walls and make it sturdy.
thanks bra..where do you put your terminals on the box to hook up the subs to the amp?..should i just run them through the port for less resistance or put a terminal on each side, one for each pair of subs