Caulking

Is there any type of caulking or silicone I can use to seal the inside seams of a tortoise enclosure?

I believe that 100% silicone/aquarium safe silicone is okay.

Sashco Lexel Weatherproofing clear caulk sealant. 2 pack from Amazon 13.77

GE Silicone 1 is the best to use for this. It is pure silicone and has no additives at all. The Lexel mentioned above is mold resistant so it would have chemicals added for that. The GE Silicone 1 should also cure much faster.

Any sealant that you use. Wipe off any extra with a rag or a sponge.
Even non toxic sealant wont be digestible. And chances are, a tortoise will eat some.