To address the area where the tanks sits on the supports I plan to glue plastic to the tanks with 5200. The aluminium will not be in contact with any surface.
I have set tanks on Dridek tiles, which works well. Only raises them about 3/8", and allows enough circulation to dry out, even if you hose the area down occasionally.
Gluing plastic to 5200 would work, if you can get the 5200 to stick long term to the plastic. I'd suggest flame treating the plastic before gluing.