You'll never be able to completely stop the rainwater running down the mast without stepping the mast. You can greatly reduce it through several methods. One is to use spartight in place of the wedges and boot. Another is to install your boot as best you can and seal it with silicon sealant. Squirt a bunch up into the mast track from below. Unfortunately, there's no real good way to stop the rainwater from entering the various holes in the mast (halyard, topping left exits, etc). Atleast, when the mast is well sealed at the deck, the rainwater is greatly reduced.
