---

The T-Topless is a nice solution like Phil mentioned.
If snorskyp's heart was set on a full T-top I would still not cut into the floor to get backing plates under it.
I would distribute the force over some wood planking running under each 2 of the legs (this could be fore-aft or sideways.
And then I would use 3M 5200 and a couple of well nuts (expansion) and SS bolts to secure the contraption to the deck.