lynall said:

It was on the underside of the gunwale where the top half of the boat is glued to the bottom so is applied upside down in quite a wide groove.
The original stuff fell out in chunks and was under 20 yrs old at the time and Im assuming a boatbuilder would have used sikaflex?

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Not sure. I seem to remember it is a fibreglass boat, and that is a material I haven't had much to do with. From what I remember, they stick a lot of things together with resin. But probably use Sika for retro fitting.

I was kind of joking, the repairs may be around in 60 years time, but I won't!
I just have a kind of obsession with over engineering things, especially boats.

Because the ally is a good conductor you will get a lot of condensation on the inside so you must either glue the insulation to the inside to prevent a "cold face" or make the lining and insulation removable. Ply lining in vans alsways has a lot of air circulation, if you look on the DIY camper converswion sites there's a lot about the problems of condensation and rot in liners. You have the other problem that you have both ally and steel so you don't want to hold any damp behind the liner. Its its noise then flash-band works well and you don't neet to cover the whole panel, if its thermal then silvered foam camping mattresses glued on are good. I have removable panels made from Correx (about £8 for 8x4 sheet) with foil bubble loft insulation and then carpet glued on. Like others have said, strong rubber mat works best on the floor, water will get under it and so you will need to pull it out to dry on sunny days so don't glue it.