What boat? Deck-stepped mast?
I'm still pining for a decent electrical junction box at the base of the mast, the top, and spreader level (or wherever wires need to go) but so far I've been too chicken to cut a big enough hole.
Not sure that the hole through my mast step ever leaked, but when I hogged it out to make room for a radar cable, I glued in a PVC coupler (male thread X slip), to make a dam. Any water coming down inside the mast would have to rise at least an inch before coming inside the boat - hopefully it finds its way out through the weep hole before that. Anyway, it has never leaked since then. But I have external halyards, so I think the mast is pretty dry to begin with.
The hole itself is "englished" to one side so that it comes out next to the compression post and adjacent bulkhead. A bit of trim made from mahogany scraps and bits of doorskin conceals it and a terminal strip
BTW, I ran into trouble using jacketed cables for the mast lights & etc. They all fit, but when the newer radar cable was just a
bit fatter, (and the mast was dangling from the $$$/Minute crane) suddenly they did not any more! I had to rapidly strip off all the jacketing (which had the
labels on it) and push through the individual wires. If one had the aforementioned junction box at the foot of the mast, all this sort of thing could be taken care of at leisure.