I just finished building my custom "Lava Tube" tank for my two European Fire Salamanders. It's 36"L x 16"W x 18" T and constructed entirely of 3/4" Birch faced plywood. I waterproofed the interior using fiberglass resin and woven fiberglass matting. I then used "waterfall" foam to further waterproof the interior and to act as insulation. I made the front viewing panel out of a piece of 3/8" acrylic and secured it with 3/8" aluminum U channel. The front viewing panel was designed to slide out to one side, so that it can be removed, and make for easy maintenance.
I designed the tank with a false floor and the area underneath it to act as a sump. The sump has a small water pump installed that feeds a waterfall and an exposed pond section at one end of the tank (It's there just in case they feel like breeding) . The whole system holds approximately 4 gallons In order to make water changes painless, I installed a 1" bulk head and ball valve on the bottom of the enclosure. With that set up, all I have to do is connect a hose and open the valve to completely drain the water from the enclosure.
Since I live in So. California and my salamanders prefer a cooler climate, keeping the temperature of their enclosure within tolerable limits was a priority. To accomplish this goal I also installed (2) 12 volt thermoelectric chillers (Peltier devices) into the top of the enclosure. The coolers themselves are rated at 60 watts each and provide enough cooling power to maintain the enclosure at 55 - 60 degrees even if the ambient temp rises above 90 degrees.
For lighting, I installed (1) 50 watt BridgeLux LED array that shines through a small opening cut into the top of the enclosure. The opening is sealed by another small piece of 3/8"acrylic to prevent cooled air loss and the occasional cricket that's looking for an escape route. I have the Led lighting subdued to a comfortable level for the animals and plants and it's all controlled 24/7 to provide daily "sunrise/sunsets" via an Arduino micro controller.
I'm going to be adding a few ferns and other forest type plants in the near future, but here's a photo of what it looks like so far.