1/4 inch thick plexi will bulge also....i assembled mine and made a top. glued the top on and with a router went around the left half leaving a 2 inch rim. then the right side the same. in the center there is a 2 inch piece that was left to hold the sides from bulging out...its the same if you have ever seen a solid acrylic tank. Im not good at explaining very well, i will draw a pic if needed.