So, after looking at this project for the last half hour, due to the sagging tank bottoms not allowing me to put any thickness of rigid insulation on them, I think I am going to furr out the bottom rails of the frame I beams with 1.5" pressure treated 2x4, ripped down to 1.5". I haven't seen anyone do this, but I think it will work.... it will make the bottom of the frame 1.5" lower, but it will allow me to put some rigid 1" insulation under the tanks and not have a huge bulge hanging down. I can use some spare Coroplast to wrap the edges of the 2x4 exposed to any potential water. It will simplify screwing the coroplast by being able to screw it in to the wood 2x4 rather than having to try to line up the old holes drilled into the steel. I guess the drawback is that the wood screws could back out over time. Thoughts? The reason I want to get away from fiberglass insulation on the bottom of the tank, was the old fiberglass I pulled out was re-arranged into nice little mice nests, and it was disgusting, not to mention, not very insulative.
