Have sailed on a lot of these smaller trailer sailors. They're fun boats.
If this boat sat outside for 20+ years in all weather
, the entire deck
and hull probably are saturated and damaged.
Repairing all that would be a lot of time and money
. It sounds like the boat is landfill.
Keep or sell the mast, sails, anything that can be removed from the boat, and the trailer. Then go buy a 20 foot boat in sailing condition.
If you really want to rebuild
this boat. Take some shots close up and far away inside and outside that show the area you're asking about. And some photos that show the inside of the cabin
layout in that area.
It looks like it could be designed with a swing keel. Go look at sailboats about this size that sit low on the trailer to see how this works. A sailboat needs a keel as well as ballast in order to sail in some direction rather than just be pushed around by the wind
Who built the boat? Is it owner built or a brand? If it's a brand there might be a stamp or tag somewhere on the hull.
The boat would have to be covered and heated in a garage or in storage
for a while (like months) so it can dry out before you could work on it.
Work probably would include rebuilding the entire boat, not just the interior
wood and adding a keel. Consider landfill and buying
a boat in sailing condition.
Go take a beginner sailing class together now. Don't wait for your boat.