795 is good but not the best. I just replaced a fixed port lite/lens on my 08 41ds. Sikaflex is the best. Along with the Sikaflex you will need the activator and the primer , very expensive but you don't want to do this 2x. Most of the fixed lites/ports/windshields are in a bed of dried compound with no mechanical fasteners. You are correct in assuming a 1/2" expansion during direct sun exposure. On my boat I didn't have to remove the AL frame /bezel. You could see the outline of the acrylic lens and I cut out the bedding perimeter to remove it. Scrape out all of the old compound, clean area throughly with denatured achool, sand the area where new bedding is to be applied, follow directions, use the primer and activator, use blue tape as much as possible on lens, AL frame. It will take 2 applications to get your lens bedding 100%. Happy days when you are complete.