phew.. gusting 60mph here in Suffolk ..it's weather to make one glad not to wear a toupée or a kilt !
So, having decided not to drive around with a garage wall attached to a timber - yesterday I straightened out and reinforced the top return flange. I also extended the boot shut return (which overlaps the drain gutter) by another 1/2". Although it's pretty close to the original steel panel, I might go back at some time to do the same on the LHS wing as this side now looks better, and it'll give me another screw fastening to hold the panel in shape.
Today having trimmed the feathered edges of yesterday's grp and refitted the top flange's attachment studs, I'm 'close enough' in panel shape (particularly down the rear door shut) to extend the rear door shut face (as I did on the LHS rear wing, from 8-10mm to 25-30mm).
^ using blue masking tape again as a temporary mould, you can see here the wet laminate of the new shut face ..with this n' that blocks, pieces of card & wedges supporting it.
The inner web that I'd been using (cutting & shoving) to get the shape 'close enough' is seen running almost parallel beside the new web. There's also a flange on the body's door shut (with the rear door striker plate attached to it) and that takes a rubber lip seal, which sits inbetween these two (grp webs) to keep rear wheel mud splatter from coming as far forward as the door shut.
The grp is now curing, and so although just 3 o'clock I'm taking the rest of the day off .. yippee