16” x 51” x 3.75"
The lift assist cylinder is anchored in rear outboard corner (RS & CS) and the front inboard corner has a triangle vertical brace 1.5" x 1.5” on the 90 degree sides.
Wine bottles that skinny? Don't know how much the plywood flexes under sleeping load. Might try taping an egg in place to measure flex, or a handful of playdough so you can measure instead of just clean up the mess
Have you considered the space between the recliners under center cushion or even under the recliners? We fit two boot boxes in the center for dry bulk staples. 14w x 12d x 5.25h (x2) will fit in the center puka. Under the recliners is a yawning chasm just asking for something.
And then there is the outdoor space outboard the refrigerator (might need a wine cellar lock on the screen door). And then there is the hidden space above the plywood top of that same access space. So much empty space driving down the road.
Disclaimer: all additions of weight to TT should be balanced fore & aft, port and starboard, not to exceed GVWR or your ability to consume during planned underways before expiration dates (not applicable to wine)