Rowly, I don't know of a plan I could recommend for your island house, they all tend to be too complicated for your practical needs. I would recommend that you plan for easy cleaning, maybe build it on skids so it could be easily moved. If you use thin plywood and minimal studding you can keep the weight down to facitate moving it around. I use a straw bedding which needs a periodic refreshing. Since you have an aerator on the island, will you be keeping open water in the island area in the winter? When your water is frozen it is a highway for predators, the open water could be the answer. In any event it sounds like a fun project, and don't forget the cylinders, they are also good weather protection.
Jim
