The mast is not waterproof all the way down, only to the point of the exit block where you insert the sail in the mast track. There is no tube there due to that reasone, just a line running down to the mast base.

The volume in the mast is so large compared with the boat weight that it is very hard to get the boat is mast down position. I managed a couple of years ago, but only when the mast was broken...

A line is cheaper and more roboust but you need lines instead to keep the pole in position and since it is a uni rigged boat with twin forestays it is more tricky than a normal sloop rigged boat.

You guessed right, there is a tube going horizontally with a sheave at each end to turn the halyard two 90 degrees turns. I haven't had any major problems with the mast rotation so far and I don't have any space left between the sheave and the top of the gennaker.

The halyard trigger line is connected to the block on the tramp. When I pull the line to take down the spi hard enough it will pull the line that the block is connected to, trigger the cleat and after that the force in the block is high enough to keep the cleat open during the "take down" process. When the spi is down the cleat will close by it self and be prepared for the next hoist. A spin lock requires a manual interaction to trigger it for the next hoist.

I agree that the poles a fragile, but repairing them is quite easy. I haven't broken any one yet....but I will sooner or later!

Cheers
Hakan