Painting or sealing the inside of a wooden stand?

[targaboy78]

Hi guys,

I am in the early stages of putting together my 175G Bowfront Reef tank. I will have a 33G sump inside my wooden stand and I am wondering if the bare plywood on the inside of the stand will experience rot or mold.

I am thinking about sealing the inside of the stand but I can't decide between a water-based Varathane or a Marine Varnish or a wood/deck sealant like Thompson's Water Seal.

Any thoughts or insights?
Tips or warnings?

TIA
Paul.