Not used the 1111 but have used other BZ products they do what it says on the tub, they have a shelf life we have found
Shelf life is important and many people sell old stuff off cheaply.
A friend of mine did something similar to repair the wings on an old Hillman Minx. He worked for an engineering company that had a foundry & they used some sort of 2pack epoxy for making cores or patterns, not really sure what it was used for. We found if you mixed it with polyfilla to make a paste it went as hard as rock, you could hit it with a hammer & it wouldn't damage it. You could not smooth it off once it had gone off though, but you had about 12 hours working time with it.
In the days of the NCB we had sausages (resin) which was a plastic tube of resin and an inner plastic tube with hardener and you put them in a hole and put a roof bolt in and drove it with a borer to burst the plastic and mix the components, filling components such as sills with this was a regular occurrence and you would often find the ends of the plastic which had been cut off from a night shift having a pit topper, one guy had an old Vauxhall Viva estate and he filled his sills and was T boned by a lorry and according to the experts this resin filled sill saved his life.