Martin Morley kept a blog over at Sceno:graphy.org (now no longer updated). He provides a fascinating look at life as a scenic designer in the UK from 1968 to the present. In addition, he has dipped his toes into the world of prop-making as well during his career. In one post, he gives a brief glimpse into how prop-making happened at the Royal Lyceum Theatre in Edinburgh in the late 1960s:

I found I had an aptitude for prop making and polystyrene carving which was just coming into its own for 3D work. This was of course long before the days of vac forming. Pretty well everything was made in house with the exception of everyday furniture which was generally trawled from junk shops and the like. Hector Riddle, the head of props was quite outstanding: I remember the Bofors gun he created for Events While Guarding the Bofors Gun was especially impressive. It was the level of care taken on the details that stood out.

The rest of the posts are equally as enlightening and informative.