Hi. Im new to this but became very interested when I recently set up a 20 gallon tank for my daughter and mounted it into the wall. Now I am obsessed and daddy wants his own big-boy tank. I wat to do a 6x3x2.5 but there is no way i will ever afford it unless i build it. I like the plywood idea because i will be building this into a wall aslo. My only concern is the waterproofing so I thought of an idea that I have yet to find a post on. here it goes. first I would get my sheets of 3/4 plywood and laminate them with formica (like i was making a counter top. then I cut the wood to the dimensions needed (this way formica goes all the was to the edges of plywood. Then I build my box uing liquid nails then screws. I would now have a box that would be water tight. Then cut the hole for my viewing window and install glass with silicone. Then go back and run a nice fat bead of silicone down all the joints where the formica covered plywood sheets meet. formica come in all different colors (including fake marble) and is fairly inexpensive. It is also paintable incase you wanted to change the color. Anyone think this is a terrible idea? My theory is that it it a continious sheet so there are less areas taht could possibly leak. at least this way if it did leak you would know it was a seam and not wicking through the epoxy.