I've pretty much decided to go with an aluminum tabernacle - I've got feelers out to multiple marine architects in the area to work up the design exactly. (I'm not at all confident of my ability to do that particular work myself).  If I don't go this route, it's because I can't get the thing designed up and manufactured for a reasonable sum.  One firm quoted me $4000 - $6000 for the design alone.  That was reduced to $2550 - $3400 when I explained that I don't want them analyzing the whole rig - just make me a box that'll hold the mast.  Still way too pricy.  Other conversations are in the works.

Assuming I can get it done at an affordable price, though:

I'd like to permanently, as in, never leaking and rock-solid attachment, install the tabernacle through the deck.  To my simple mind, that means a solid connection to the partners, then thickened epoxy fillets with biaxial glass tape running out on the deck maybe 6".  Just like tabbing in a bulkhead, only topsides.

But... Am I asking for trouble over time with the heat cycles and tiny flex loading cycles?  A failure in the glass/epoxy to aluminum bond will let water into the hidden spaces and lead to undetectable corrosion.  Does this fall into the same category as, "Never glass in your chainplates?"  If so, how does the collective mind suggest I handle the tabernacle to deck seal?  Also - if corrosion in the deck area is concern, how the hell do I inspect that every few years?  Can't pull it out like I would a chainplate.