Hi Andy
Here is a picture of my rear tub, sorry it is not very detailed though.
I found it one of the easier parts of the build to do.
Didn't bother with the book template as the rear hoops were made to a profile that was pleasing to my own eye
Started off with a flat blank that was a fair bit over wide & over long.
Marked the centre of the blank & Clamped it to the rear framework .... You'll find some long reach clamps handy for this job, don't forget to pace a strip of softwood between the clamp and outer face of your blank, this will protect the surface finish,
Once you have the blank clamped in place securely you should be able to bend each corner around the rear hoop.
Just make sure that you keep a little pressure on the side of the blank as you work round each corner section ( I just kept the side of my leg in light contact with the blank but you could just as easily use a small length of softwood ) .
Once each corner was fully bent tightly around I clamped the end off on one of the frames.
With both ends fully bent & clamped I was then able to mark the cut lines & once marked, I removed the clamps to release the rear panel then cut with a jigsaw.
The straight sections of the rear hoops you can leave aproximately 1/2 -3/4 of the tubes circumference over long as this will fold around the hoops very easy with the help of a rubber mallet & wooden dolly .
The curved sections need to be cut a fair bit shorter, I would say, slightly less than 1/4 of the tubes circumference, these corners should fold over with the help of a flat panel beaters hammer ( Slowly, slowly a little at a time )
If left over long the curved sections will wrinkle up as they will be in the realms of needing a shrinker.
Very pleased with the way mine came out, no tooling mark to be seen
Might be obvious but top tip here.
If your lower rear hoop sticks out further than the top one ( Sloped back )
Just remember that the flat blank drops down a fair bit as you bend it around the corner so keep most of the over width at the top.
Got the first scrap attempt as a reminder of my lack of diligence
Hope this makes some sense to you.