1. 1/4"
2. Methylene Chloride and/or weld-on
3. put it together.
Seriously. If your cuts are square it will go together square as long as you are careful.
I built mine in the stand.
put bottom piece in. Attach one side with a small drop of methylene chloride on each end just to hold it. Put end in place. Hold the end to the side run meth down the joint where they meet. Make sure they are properly together. not overhanging. Attach other side in same manner a first. Bond joint of the singel end with the side just placed in. Once they are bonded place the remaining end. Once they are all fitted together nicely run methylene chloride aroudn the bottom to seal it all together. Than fit baffles in place and bond.
take a read of this thread. I give acrylic sizes etc. Easily modified for any size stand.
http://reefcentral.com/forums/showth...p&pagenumber=2