More messing about today.
First up, replaced my swimming pool lid with a reinforced commercial one, but when I was at it stripped it, and did both sides with the insulation and then taped it up also, might help a little.
So that's good, next up I had really wanted to bed liner the rear panels but for all I use them it will be fine, so I reached for a tin of hammerite satin black and started rolling it on. Pics are taken over 3 coats and I'm happy with even result, it seems a bit more glossy than satin overall but see when fitted in van I'm sure be dark enough!
Better than that god awful oem colour in the rear, and I'm too tight to buy some later panels in black.