I may be kinda old in my ways but I ues 3/4 MDF held together by Elmers wood glue, lots of it, and drywall screws. I have noticed that a lot of people on here use all sorts of different thigs to seal their boxes but the Elmer's has never let me down. If I have box sides that are on the larger side, or using a large amount of power, I make a braces out of 3/4 MDF.