Planted Tank Guru
Join Date: Jul 2008
Location: East Lansing, MI, USA
Lap joints or butt joints?
Either should be fine, but I'm guessing butt joints as you are having Lowes cut the wood for you. Especially since you are making this a double box, half inch plywood will be plenty. Except for the 3/8 round over quarter inch would probably be plenty for a five gallon tank. Double 3/4" ply would be overkill.
Plywood routs fine - but. There may be voids that you will have to fill. Such is the nature of the product.
I've never used a two part epoxy coating. The video at the home improvement store makes it look easy. Since it appears to be self leveling, I'd suggest you practice on some scrap first.
Personally I'd start over on the plans and save even more wood. You really aren't looking at much weight. Properly glued, an interior frame of 1x skinned with 1/2 inch birch plywood will be more than sufficient. I think you could probably get this down to half a sheet of material and have pieces for shelves. With cabinet grade birch plywood and not birch veneered whatever, 3/8" would be fine.