Waterproofing rudder trunks

For reasons that are currently Extremely Secret (i.e. until I get the bugs sorted out or summon up the courage to make such an outrageous idea public) I want to have a rudder stock that comes up within the hull and stops short of the deck, so that the steering gear is below deck level. The problem is to waterproof the top to stop water getting into the boat.

The rudder stock will be carbon rod and the trunk pulltruded carbon tube. There is nominally a clearance of about 0.05 mm between the trunk and the stock, but because of the slightly rough-and-ready nature of the carbon pultrusions available it will almost certainly be necessary to sand the stock slightly got get a good non-binding sliding fit. Given my primitive craftsmanship this will almost inevitably result in increased clearance in places.

I propose to make a candlewax top seal for the trunk - just melted on and the rudder stock then broken free by twisting. With a washer above it, this should also at as a low friction thrust bearing cotrolling vertical movement of the stock.

Anyone see any problems?

Unless you cut the rudder tube very short, the top should be able to be above the waterline and so, not leak. However, you could smear some grease or vasaline on the shaft to act as a barrier.

Prather Products flex shaft lube (blue grease), should do the trick.

I would keep it simple and do as hiljoball and roadtoad say. Unless you do have to have the tube really low.

I suspect that a candlewax seal would break away in no time, maybe try beeswax if you must?