17 August 2022. Several kind people have expressed concern about the pressure of the expanding foam.

The centerboard trunk did withstand the pressure of the expanding foam with a good margin.
To tell the truth I did not think that it would be a problem but when surfaces are concerned even a small pressure over many square centimeter gives a lot of force.
The Magdeburg hemispheres, around 50 cm (20 inches) in diameter, were designed to demonstrate the vacuum pump that Guericke had invented is a good example. One of them had a tube connection to attach the pump, with a valve to close it off. When the air was sucked out from inside the hemispheres, and the valve was closed, the hose from the pump could be detached, and they were held firmly together by the air pressure of the surrounding atmosphere.
The force holding the hemispheres together was equal to the area bounded by the joint between the hemispheres, a circle with a diameter of 50 cm, multiplied by the difference in air pressure between the inside and the outside. It is unclear how strong a vacuum Guericke’s pump was able to achieve, but if it was able to evacuate all of the air from the inside, the hemispheres would have been held together with a force of around 20,000 newtons (4,500 lbf; 2.2 short tons-force), equivalent to lifting a car or small elephant; a dramatic demonstration of the pressure of the atmosphere.
The wonder of vacuum.
Exlex centerboard trunk have 30 millimeter 200 kilo/cubic meter Divinycell sides in addition to that overlapping there is another 80 kilo Divinycell sheet overlapping making a total of 60 mm Divinycell sandwich constriction.
The hull of 60 feet production boats commonly use 20 mm 80 kilo divinycell in their hulls.
I have done a bit of cleaning up and shaping and drilling the hole for the strongpoint of the centerboard.
Not very exciting but things needed.
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