Silicon and the screws... yes. The silicon will be on a wide 1 to 1 1/2 lip under the cover. This wide lip exists all around the top of the tank, the cover goes down into this recessed area and rests on this wide lip. Currently I am scraping silicon out of that area so I can use it again to seal the whole thing back together.

I suppose I could use some sort of gasket material...

Or some other sealer.

But that wide lip and a lot of silicon seems to be pretty effective. Of course there may also be a better solution...