Decided, glass and no hatch!

I made up my mind and may thanks to commenters and the kind folks over at Wooden Boat Forum for their input.

First I'm going to use 4oz fiberglass cloth to cover the areas under the floor. From the bottom up to about 6-7 inches is glassed in. This should be more than adequate to keep any moisture damage in check.

4 oz fiberglass ready for epoxy on the keel backbone side. 

Then I covered the bottom of the floor with 4oz fiberglass cloth.

Floor bottom covered in 4oz fiberglass

After much internal debate I decide to K.I.S.S. The interior glass on this compartment is going to keep it rot free for may decades, probably beyond the point when the pine box I'm in the under the ground has rotted away. Unless there is exterior damage, in which case I'll just cut out a hatch when I need it.

The floor wasn't cut tightly to fit, it's really not necessary to have very tight fits since there needs to be room for the epoxy, so I used a couple wedges to get the sides bulging a slight bit to give a nice fair curve. I had spaced apart the hull sides when I installed the stringers but it didn't hold most of the curve so I put the spacer back in then the wedges.

Dry fitting aft floor

I'm happy with the dry fit of the floor, but no epoxy fillets today. It is late September and the maple leaves are turing beautiful colors, also the outside temps are routinely hitting the low 40s at night.  The garage has no central heat so the temp has been easing down and now it hit 60F. It was after noon and I didn't what to turn on the portable heater since it would take a couple hours to warm things up. So tomorrow I kick on the LPG heater early.