?The best finish to reduce expansion in moisture changing environment?

The Project
I am building a cockpit table for a boat and using an unusual combination of woods; a glue up of 2-inch wide strips of quarter/rift sawn white ash with 1/4 inch mahogany strips in between. The table has one 12 inch by 24 inch with two fold-out leaves 6inch x 24 inch. The table will get a lot of harsh use; exposed to severe climate changes, on occasion get wet from rain, and will no doubt have a few drinks spilt on it.

My experience with finishes
I have never been satisfied with the durability of spar varnish finishes in harsh marine environments however I have had excellent results using multiple coats (10) of tung oil (LeeValley brand) on a teak/holly boat floor with great durability and repels moisture well. I also have a lot of experience with epoxy for FRP lay up and adhesive repairs but never as a finish.

My questions

To reduce the risk of cracking from expansion in the severe moisture-changing environment I plan on first completed finishing each piece before hardware attachment.
Thoughts on this strategy?

What are your thoughts on an epoxy vs. the multiple coat (10) tung oil finish mentioned above.

What is a good epoxy finish brand/product?

What other finishes would you consider?

Thanks,

Ben

You shouldn't be focusing on eliminating moisture exchange, but should focus more on designing so that nothing adverse happens when the wood undergoes seasonal shrink swell.

Spar varnish isn't very durable under foot, the teak and holly deck works fine with the tung oil largely because it gets little or no regular direct sun, being below decks I presume. (The floor of a boat or ship is the planking just above the keel, the other things you walk on are decks.)

But in the cockpit, sun becomes the enemy. You can either use a Sunbrella cover to keep the table out of sun when not being used, or you can use Spar Varnish to resist UV light as much as possible. But, only use good spar--Epifanes Gloss, Pettit Captain's, or Interlux Schooner. Take heart that a table will take much less abrasion than a floor, making the spar more durable.

You can slow moisture transfer with epoxy, under spar varnish. The spar is still needed because epoxy is not UV resistent. You want a low viscosity epoxy so that it penetrates the wood. Smith & Co. makes some (available through Jamestown Distributors and good marina's.)

I went over to the "shrinkulator" and found that white ash moves almost twice as much as mahogany in response to changes in moisture content. That's going to put a lot of stress on the glue joints. Assuming the table top is relatively thin, it will probably be ok, but using either the same kind of wood or woods which match more in their response to moisture would be safer.

Another approach might be to put a thin layer of fiberglass over the table, then epoxy over that, then spar varnish. I have used West System products and they give good instructions on how to do that.

But the glue joints will all be side grain to side grain. The movement problem is in the thickness, perhaps using the ash turned the other way, flat grain up, and the quarter sawn grain on the sides, will balance it better against the mahogany. But at perhaps 3/4" I don't think there will be very much of a problem.