Thanks Terry for the answer!

First, it must be made rigid, so it does not move. Wedges, spacers,
adjustable clamps, whatever, at top and bottom.

The keel was inserted into the keel well, fiberglass was put on the sides of
the keel, and finally bolts are put through the well and keel and tighten
the whole thing togeter. There is no movement in the keel to be felt. Mats
of fiber are put under the boat and closs the gap between the keel and the
hull. Put I "touched" some rocks and this seal was broken (lasted two
seasons).

Will it be exposed to freezing while afloat? You don't want water
freezing inside an enclosed space.

Excatly.. That is my problem.. I am also afraid that there might be non
visible leakages inside the keel well. The well is built with wood that is
sealed with fiberglass. But what if it is a leakage from inside not visible
to the outside. Slowly the whole well will rotten from inside... Not good..

Do you want to be able to remove it again?

No

I think the problem is that there is some movement (very little), but enough
to break the seal I made last winter. I only applied some epoxy without
using mats. When the boat was put into water the keel probably moved a
little and broke the seal. I am thinking about swimming under the boat and
applying some epoxy-kit while the boat is in the water. Maybe the keel is
now stable and this seal will keep water out during this seanson..... Later
on I will aply some mats....

Anyone applied epoxy underwater? I will first remove the antifouling, and
the try to apply it. I have to wait for the water to get a little hoter. It
is cold here in Norway..

Haakon