If not using a "Myers Hub" or a sealing ring (which looks like a washer with a rubber gasket on the I.D., see link below) I believe any conduit joint will let water in at the point which it mounts to the enclosure.
As far as WP hubs, although the WP connector's threads are not tapered, the hubs might be. But anyway, the bottom of meter enclosures will let water escape and it should not accumulate.
I know it is not a sealant, but I use Noalox to lubricate WP connector threads. It lets you engage more threads, and probably helps keep water out. After all, we are not talking about pressurized water lines. http://www.tnb.com/ps/fulltilt/index.cgi?part=5264
[This message has been edited by Redsy (edited 06-03-2006).]