"I would like to save them if I can, the shell is very hard so I don't know until I try."
You have just answered your question yourself.
For your own interest and anyone else: I have used Plaster Cloth for many years my method is a bit over the top but it's certainly strong.
The method that I have used for many years is below. I read the original idea in a Marklin Magazine years ago.
Using any kind of support I like newspapers as well, cover the newspaper with the plaster cloth then mix up equal parts Polyfilla,(like plaster but slow drying) cheap white glue, water, and a dash of coloured water based paint, I use grey, then paint the plaster cloth and apply a layer of cut up paper towels that are cut into 3inch squares then cover again with the mixture this results in a rock hard scenery base. Roo.
