Eggcrate

[sphelps]

Aluminum will not rust or corrode so you don't need anything with a coating, it may be better to avoid a coating as it could come off and fall into the tank. Plain old aluminum would be best, when exposed to air a layer of aluminum oxide will form and protect the metal from corrosion, just keep it out of the water and you'll be fine.

[hillegom]

All aluminum fish boats and aluminum lower legs have a piece of zinc attached to them.
This zinc becomes the sacrifical anode and corrodes before the aluminum. If you did not have this sacrifical anode, then the aluminum would oxidize and eventually the high priced boat would sink.
I would not use any aluminum anywhere near my aquarium. Splashes always occur.