I have an interest in metal boats. I read a book written in the 1970s by a British author who went to the netherlands to get up-to-date on the best metal boatbuilding methods used by the world's experts. He enthusiastically championed sprayfoam insulation which was being used nearly universally by the dutch at the time. The boats that got sprayfoamed invariably had short useful lives and horrible corrosion problems. It is no longer considered a good insulation method in boatbuilding.