Slate Floor - sealing the edges

Hello,

I'm going to put a slate floor to cover all the bottom glass on a tank for an Axolotl. It'll be in 2 pieces so as to be able to get them placed easily.
I want to seal around the edges so it doesn't become an anaerobic refuge in the small voids under the irregular slate bottom.
Which would be better to use - aquarium-safe silicon or aquarium epoxy? It sounds like the former doesn't stick well to slate and the latter doesn't stick well to glass! I'd prefer to use the epoxy due to faster curing time.
Perfect solution would be an old metaframe tank but I never see any 50 gallons.

Thanks in advance for your help.

Alternatively, has anyone made any sort of cork floor for their aquarium?