That's thinking outside the box if not the TUBE!
Nice pattern tube - haven't seen it before.
Couple things: you know it's dangerous to cover stainless with plastic,
salt water will get in where you terminate the encapsulation.
MAYBE cleaner install can be cap screwing - through the deck - into the tube strongback inside.
Or even through bolting the tab, through the whole strongback tube using tube liners for the bolts as one does when thru bolting a mast - a avoid caving in the sides.
Any future leaks will be a heads-up that maintenance is in order!
The other thought is
that when you see European tabernacles they often hinge the mast at the top of the
tabernacle. This may allow AFT lowering visavis over your dodger to a boom gallows eg. Or if FORWARD lowering the mast won't be at a crazy angle visavis the the pulpit where it has to rest.
I'd guess that the mast at an upward angle on the pulpit will create some strong leverage on the pulpit and at the bolt end as well.
A lower angle of the mast when down will make unhinging the mast easier because the mast will be more level. Also reattaching the mast - as the mast's fulcrum is the pulpit - where the mast is 2/3s outboard - it's heavily weighted to falling further over the bow.
With a tall tabernacle aft lowering is preferred I think,
as more of the mast is inboard when lowering and when resting on a much more substantial gallows.
Interesting to see what you come up with!
Certainly not going to have any compression issues ever again!!!
Good tabernakling !