Large delay to respond - sorry bout that - I actually just did a tank clean and remodel. I bought two 20 gallon aquariums for $14 at Walmart. With gloves on, broke the end glass out of one of each with a hammer (in retrospect, I could've just used a box cutter blade to remove the glass...), used box cutter to clean all silicone off the edges, and glued them opening inward onto a flat whiteboard cut to accommodate the size of both. I used industrial strength adhesive to bind them to the board, and then used silicone in multiple layers on the bottom edge to seal the bottom joint. I made sure to keep the black plastic under-supports, so there is support in the middle of the tank along the joint. I cut a strip of acrylic and glued it to the inside along the up/down seams (the idea being to keep the joint from moving too much), and then added multiple layers of silicone over the top to seal it.
I also sealed the pump portion of the (usually over-the-side) aquarium filter, to enable it to be submerged. Using hose, pvc T-joints and plastic screen, I made an under-gravel filtration system pulling water into the filter. Added a small layer of gravel, then some bio-degradable landscaping fabric, then more gravel. Built it up so there is a side that's lower, but for good measure, put a plastic basket and plastic cutting board to elevate/stabilize the land-side. Added a saved mix of springtails, woodlice, red-wriggler and garden worms, then new repti-soil, rehydrated moss, and coconut fiber over the top.
Got a vine and fern from home depot, rinsed the roots, and planted them along the edge. I used the cut end of a mesh basket to form a little holder flush to the aquarium back, which serves the purpose of keeping Sally and Mander from burrowing in it. (Mander decided just to lay on top of it this am...). I'm in the process of creating pvc half-pipe logs for hides, and am waiting on several shades of Krylon Fusion paint to be delivered today.
All in all, it seems to be doing well.
(Krylon Fusion just arrived while I was typing this. Will post pics of hides after a couple of days and paint has cured)