With the basic GRP set joining the two pieces, I added some more to join the curves on the sides, to give them some strength, and also for something to prevent the bodyfiller from going through.
With that set, I saw that the curve wasn't as continuous as Id've liked - although it doesn't really matter in the grand scheme of things (you aren't really going to see it).
But that didn't stop be putting some thicker bodyfiller over the join. I also drilled out the rivets.
I sanded down the bodyfiller:
However, it's not wide enough - the wheel is 245mm wide, while this is 240mm wide. So, I needed to widen it. I decided that the best way was to cut it into two lengthways, and join them with aluminium strips (like I joined the two cycle wings, but width-wise), and to fill the space, something with the same kind of curve was required. The best thing with the right curve is the inner wheel arch itself, so I used it as a mould. Since I couldn't find my mould release agent (PVA), I used some kitchen foil instead - this has the advantage in that it doesn't stick to the inner wheel arch.
Using some 50mm wide strips of chopped strand matting, I made a new curved piece:
All that's left to do is to cut the wheel arches and join them back again. I'll probably make it 30mm wider.
And then work out how much is needed.
And then get John to make some.