The bulk head insulation has a foam backing that seems to be open cell sponge: ~
Not a good area for the above because of the dampness- I removed the original and replaced with Hardura- use the old one as the template.
Prior to replacing coat the bulkhead areas in your favourite rust treatment-Waxoyl or similar.
Hardura is a PVC insulation product with a felt material backing- give the backing a thorough coating of the wax to repel water/moisture.
Trust it helps, Bob.
Classic car trimmers will supply
https://www.woolies-trim.co.uk/category/127/hardura is one