what about two cowls similar to what you have already made but that follow the same profiles of the top of the seat backs, in width and height.
Thought about that and mocked it out with card, but without corresponding humps in the scuttle, (like MG TD) it made the scuttle look odd.
Plus I am trying to make this a bit different.
I'd love to know how you formed that Dave.
I would like to say that it was beaten from sheet but I cheated. It's a much reworked section of spare wheel well.
That would be fine if it was a little longer.
That is the next step to try. Use the front half or so and extend the rear tapering back down to the lid. I can easily mock this up without cutting what's there.