I have a soultion from the Outside.
I have a quite old AVONB Searider. Boats of this size can't be shaken around to distribute some sealant. The solution comes from germany, at Coelean ( www.coelan.de
Email: firstname.lastname@example.org ) they sell a one component PU paint, which is super flexible. They also offer a primer and colour pastes. The result on my AVON was really good, Treated parts are sealed, also the fresh painted appearance is really good
If you need further information mail or post