Well it would seem that I'm an idiot, because all of the prop tubes in all of my models are held in by body filler from Supercheap Auto Australia, which is similar to Halfords in the UK. I had reason to remove two in the one boat recently, and it took me the better part of an hour to do so, without destroying the hull. I had to use a combination of a Dremel and a chisel to get through the filler which, by the way, wasn't fibreglass. There are obviously different qualities of body filler available, so you may need to reconsider your statement, Dave.
Peter.