From what i was told, the bubble wrap thing was to ventilate rather than insulate as the gaps between the bubbles let air through to dry out condensation.
Otherwise condensation will build up cause damp and eventually mold and mildew.
We use bubble wrap, too. For the first time this winter just gone we didn't put the winter cover on and just left the transit cover on. I wish we hadn't. I wish we'd put the big cover on as the transit cover seems to have suffered quite a lot with discolouration/fading and the elastics seemed to have suffered. This winter will be putting the big cover on again, with bubble wrap under the transit cover and tilting back.
I just put a couple of old feather pillows under the cover and open it up every so often when there is a dry day.
It coped very well last winter, no mould damp and smelt really fresh.
John
Some years ago, Barons imported some of the Coleman range of folding campers. These have used Sunbrella 302 acrylic marine canvas for many years.
They didn't sell very well, and Barons Chorley bundled up the units they had left at the end of the season, and sent them up to their Darlington site. This was in September/October, and the units sat closed and untouched until the following April.
I was there when one was finally opened up - and the canvas over the bed end was full of water. Clearly, it had been raining when the Coppull staff had closed it (they had no interest in them, and regarded them with undisguised contempt) and had remained with a puddle of water inside for at least 6 months.
Result? - nothing!. No mildew, no staining (some dirt marks cleaned off easily) no damage to the canvas whatsoever.
Although unintentional, it was a graphic demonstration of the benefits of Sunbrella fabric. With cotton canvas it would have been goodnight Vienna...