I posted this problem long ago and I am still fighting the issue. I had discovered water leaking from the edges of my cabinets last spring, I took off the doors and drilled into the cabinet edge and discovered water. I believe I have taken care of the cabinet issue, but I drilled about a dozen 1/4in. holes in the fish box and let them drain all summer. Recently I drilled out a one-inch hole through the fish box wall, leading to a foam filled chamber, that was completely dry, next to the other holes in my fish box. (I need to post a photo, as this sounds confussing) The wall core is 3/4in plywood, it is moist around the cut edge. I have been baking the fish box with a heater most all of the time. It has produced gallons of water over the course of the summer from just a dozen 1/4in. holes. The fish box wall is also the wall under the cabin door, the main bulkhead dividing the cabin and back deck.
I have gone through everything and cannot find a entry point for the water, all chambers are dry. I have narrowed it down to that one wall or section has water in it. This makes no sense! Any thoughts?