We are planning to replace 10 seacocks on our 45E this spring with Trudesign, (I have all of the bits ready!). Their instructions are quite clear, fit the skin fitting with sealant, apply a little sealant around the skin fitting internally, hold the fitting still (they supply small tools for preventing rotation) and hand tighten the back nut against its washer, wait until the sealant has cured (24 hours +) and without rotating the skin fitting tighten the backnut to the recommended torque (=<15 ft lb). The washer under the backnut ensures that the nut is not stuck in the sealant. The idea seems to be to form a sealant gasket and then gently tighten up on that gasket without turning the skin fitting. Clearly any rotation of the skin fitting after the sealant has started to cure will break the seal and probably result in a leak.
https://trudesignplastics-com.s3.amazonaws.com/documents/docs/57/6389b4fd615839f67ea01c49a9b9c545.pdf
The membership association for owners of Dufour Yachts