what material is that you have to cover your board? is it like vinyl or something? and how did you go about getting to conform to the openings. the way i see people upholster seats on TV is they heat the material up with something like a steamer to make the material more flexible and then pull on it to wrap around the edges cleanly. im building my box myself too and have a vinyl type material thats going on the box and it needs to cover the edge of 2 opens just like you have.