[Overdriven]

I've never had an issue with anything getting inside my FLM bulks. I've run through water, let snow melt on them, fine sand, never found anything inside. If you're worried about it, I'd just smear a super thin film of silicone on one half, bolt it together and wipe off any excess. Last thing you want to do is start modifying the mating surface. Its perfectly flat because its cnc'd, you're almost guaranteed to mess that up trying to do anything by hand.