On the stand under i used 2\6, and crossed over with 2\4 on the top. Should hold pretty good.. I have read so many threads on here about leaks, and im planing on doing this just 1 time, so better safe then sorry..The boards\plates are 18mm OSB plates as they are named in norway,but 18mm should hold pretty good! Tonight im going to make the front and put the walls together with plates. After that i need to find something to cover the screw holes and in the seams.. I will put 2 layers of fiberglass in the entire tank.