Formers:
It is worth mentioning that you can put parcel tape on almost anything to create a former of the required shape.
So I have used beer cans to create cut outs in the body shell for my exhaust pipes.
Modelling mesh to repair a curved corner section of my body shell.
Even a pink yoga mat to create a curved valley in my bonnet (after I had chopped it into two pieces).
Building the join up in stages.
Because the inside surface is where you are working, the sunny side of the former can be a real mess.
But once you have added the strength you need to the underside, you just need to finish off the sunny side.
And finally, I found a roll of ‘Builders Band’ to be very useful for holding complex shapes together.
Note: I’m happy to delete these two posts if they are a distraction from your thread, but I hope that helps.
Good luck, Paul.