What I did was build an "interior" box of acrylic laminated to wood with adhesive. It stuck tight, and the wood is providing the structural support. Then more wood was added as a base and to support the lights. I only used silicone to seal the seams on the inside of the box.
If I can't find the leak (which I suspect is the drain), what I probably will have to do is build another acrylic box using solvent weld, make sure it is watertight, then laminate that to the wood base and end pieces.