you honestly do not need internal bracing, it does not ad structural strength unless built to do so. Building it to do so would require it becoming a frame which would have been much more useful to build around rather than into. An external pressure frame would be more useful for what you are going for. It prevents the flex from the outsie rather than the inside, double bonus, no extra drilled holes. In fact you are flirting with disaster adding more drilled holes, they are the truest weak point in a build. A lot of people have had to scrap one or more walls on their build and cut new ones because they pokes a hole through the sie while pre-rilling holes because they were just off center. .. gl on the build