Anchor surplus near me does 3m strips (see pic), but 8/9quid each
Cut a section off that for this cover because I had to remove some of the outer skin to repair the rotted steel behind it
Quite easy to make up with an angle grinder or jig saw, make a cardboard template first and away you go
Must have a company that works with this stuff, failing that try a commercial vehicle breakers yard, lot of fridge wagons and trailers have this stuff in them. Also any company that constructs fridge truck bodies or trailers