The footings and PVC track system that I built saved me in this side. It was just a little off square. With the footings, tracks, pocket holes, and a lot of silicone it snugged up nicely.
I did it this way because I felt that sicking my arm down was n this thing to smooth out silicone would be WAY easier than trying to epoxy and fiberglass it.
This side will be the return from the Fx6 and Sp6. Out of view there will be three 1.5" bulkheads for a smooth return.
Small emergency spillway, that I doubt I will need was also cut out of the top.
This box will also house the heaters.