Looks pretty horrible and disgusting i kinda regret looking at this topic
I guess in a basic shed especially seperated from the main home it can happen not really recommended to store these kind of things. that must have been a terrible shed wich usually is just for gardening equipment etc the insides are pretty much a warm home to the outside elements and living critters of nature.
I've visited some people who had stuff stored in their seperate sheds and man did it look terrible, the carboard was wasted, way to many outside elements and temperature chances that effect the inside of a normal shed i guess
If you ever decide to store these kinds of things in a shed especially a shed wich is just for some basic storage affected by the outside elements at the very least cover them consoles fully in plastic that way storage would have been a bit decent even in a shed like that. only Temperatures might have damaged them from the inside but nothing else.
Not sure if it would have prevented mice though some bad luck i guess.