Another short progress report.
I have determined that 15thou Plastikard gives the best results, 10 thou thickness is too prone to blowing through before the full shape is taken up. I have also learned not to panic while using the hot air gun. What happens is that the Plastikard first bubbles and deforms, then it flattens out again. If you keep applying heat then it starts to sag and its when you can see the highpoints of the underlying mould appearing on the surface that you hit the power on button of the vacuum cleaner. The plastic is now suitably soft and a good result can now be obtained.
I have now made the first half dozen canopies and built supports for them from Microstrip.
Now that I have drawn out a plan for the market in the available space I find I don't need quite so many, about thirty rather than fifty. Still a bit of a task but nowhere near the work it would be making each canopy individually from scratch. The big task will be populating the stalls with goods on sale and people.
Just for reference, this link should bring up a pic of what I am aiming to create