Today I had another major reorganisation in the garage, so I could find somewhere to place the canopy. I evenually made space to erect a workhorse and put a large piece of packing case sheet on top. I screwed batten to three edges so that the canopy could rest on this without being stretched out of shape. See Picture 3.
Pictures I and 2 show the first trial fit of the canopy. It was basically oversized in all dimensions, ranging from virtually nothing to around 1/8 inch. I used a fetching colour of low-tack painters masking tape to identify exactly where material needed to be removed.