Yesterday I did an initial preview of the backdrop.
First I cut and pre-drilled 2×5 aluminum corner pieces and placed them on the back of the woodwork of the modules with a 4mm gap for the backdrop to sit in.
The material I used is 4mm flexible marine wood so it curves around the corners and for the whole surface it took 4 pieces about 2.2m long and 49cm high.
I will then remove the leaves, place alignment and interlocking slats on the back and paint them sky blue for now, in the future I will decide whether to paint it or use photo shop editing.