The stock sprokets should not be an issue with the metal gear boxes. We all drive our tanks without sealing things up completely outside and that is never a problem.
These are not designed to be driven through deep water in any situation.
It can be a quite complex operation to make them water proof, then you add the problem of heat build up on the electronics.
As Benny said just get your self a decent charger and some high capacity NiMh. batteries, go outside and have some fun.