Shrew said the deck has enclaspated marine plywood so yes there is wood.
To remove the pedestal you will need to have access to the nuts underneath which you said you don't have. Do you think it's possibly to drill a hole in the ski locker to gain access?
The wood will be wet, dark, and may crumble.
Yes it's a big job.
How much wobble are you talking about? Any on the other side?
If you bounce on the deck near this seat does if flex?
1997 2400 SCR
5.7 Vortec / Bravo 2