AA62, your detachment was not as deputy to a certain portly navigator wing commander was it? I remember his being extremely concerned when he returned and complaining that the underbelly protection that Marshalls had developed made the aircraft look very untidy.
You will recall the original version was a bit like Marley floor tiles glued to the underbelly of the aircraft and he was not impressed that they worked loose and, in some cases, came off. He took a lot of persuading that, as with the space shuttle, they were meant to be sacrificial rather than the aircraft skin doing the same job. The need for protection came about from Op Bushel after which an eagle-eyed ground crew spotted something amiss with the underside of one on the line at LA, investigated and poked his thumb through the skin with no effort at all - the shale on LZs having abraded it thoroughly. If memory serves we had several aircraft grounded immediately and several more flying with restricted pressurisation until repaired.
The other "skin" problem we had was with grains that had escaped from their packaging and fallen under the cargo bay floors. There in the dark, warmth and damp of the underfloor heating they germinated freely with their roots forcing themselves between the fuselage ribs and skins tearing them apart. Yet again a demonstration of the Law of Unexpected Consequences.