I would have thought that quilts would just absorb any damp/moisture and maintain a damp atmosphere? Something that mould spores would love!
The only way is to have good air circulation ... bubble wrap or create 'space'
Luckily not had this problem, condensation is formed when warm air hits cold. So check your getting good ventilation inside, like Kelper states., and a no no to duvets excellent breathing ground for mould.
I jack my pathfinder up as high as it will go at the top so any moisture runs off the back. Then I put a blue tarpaulin sheet over it then the pennie winter cover.
Also a good thing to check is make sure the toilet water is empty and the cassette itself and all water in the taps.
I forgot once and did have a bit of condensation inside, so I make 110 per cent sure now.
Hope helps in some way.
------------- Up there for thinking, down there for dancing. 😎
Thanks everyone. We haven't had a chance to open her up again, but the bubble wrap is sat waiting to go on. We seem to be following most of the advice on here already so no idea why the condensation.