Hello Allan,

I tried your method when I built my boat few years ago.
I used to have a webpage which shows exactly what I did,
but I hosted it on a free hosting website and it already
went of the net.

Anyway, the important thing is that this method doesn't
work so well when using internal bungies to pull down
the lead, and the reason is the force needed to pull
the lead down.
Think about the elasticity of the gasket and how much pressure
is needed to squeez it just a little, to get a tight seal
all around the lead. It's probably not alot of pressure,
but multiply that pressure by the surface of the gasket
and you'll get more kilograms (pounds) then you want.
You'll need allot of tension on the internal bungies
and it will be evry hard on your fingers to open and close
the lead.
I think it will also not be comfortable with any type
of external locks.

To my opinion the "propper" way to achieve a tight seal
is as follows:

1.
Create a thick internal leap, to maintain the deck
form, just like you did.

2.
SEPARATELY build the lead.

3.
Cover the internal leap with thin sticky nylon (Saran Wrap).

4.
put thickened epoxy on the internal sealing surface of the
lead, and put the lead in its place on the deck.

5.
lock the lead in whatever system you have installed, and wait
for 12 hours.

6.
The epoxy will not stick to the thin Nylon so after 12 hours
you can just remove it.
The fit will be perfect !! and you'll not need any rubber gasket.
Just putting the lead on the openning will give you aperfect seal.

7.
The thicknes of the sticky Nylon is approximately 20 microns
so it is negligable.
Make sure you make a test and verify teh epoxy doesn't stick
to your sticky Nylon.
I used a regular sticky Nylon I got at the grocery store.
I tried to glue 2 pieces of plywood with that Nylon between
them and I used "C" clamps.
I used this method to seal the joints of my 3 pieces kayak.

I hope this is helpful to you.

Erez