Our presenter seems to have a poor understanding of the collection, I'm not sure how quickly they could be mobilised 'when the stuff hits the fan'.
There are three Mk 2 Pigs. One has a canvas fitted for the roof of a Mk 1, the purpose of that is that it rests on rails around the top edges of the roof thereby providing a layer of air to try to alleviate some heating that the crew would be subjected to in the tropics.
These were never fitted to Mk 2 Pigs as they have no such roof rails & they deployed exclusively in N.Ireland that does not normally suffer from tropical heat. Apart from the fire risk in a riot situation, if they are planning for a NBC situation a canvas is not helpful either. It looks like the other two Pigs each have a canvas folded up in the back ready to be fitted once mobilised, how daft.