Truck'n'truck,
You raise some interesting points here, and if I can persuade you to get out of that attic and your grandmothers Sunday best, then I promise never to introduce you to Sally Fields.
The biggest variable here is, unfortunately, the ambient temperature (wouldn't that be a great name to change to by deed poll? "Temperature's the name, Ambient Temperature..."). It can be a real scorcher or a little parky, so that would effect your calcs. I'd say fridges are damn good insulaters, and I can't see a bit of bubble wrap making much difference. And if the beers aren't warm, what the hell are you putting them in the fridge for anyway?
It's a hairy old walnut though, and much web time has been wasted, uh.. sorry - invested in the problem. My own thoughts are:
Get a top opening fridge.
A fridge freezer would be best, get the b*stard chilled right down during the afternoon, get some beers in before bed and then switch your genny off for the night. Blast it up for an hour or two in the morning to get the breakfast beerage at the right temp. Max temperature setting during the day in a fridge freezer shouldn't freeze things solid.
With a fridge freezer you should be able to freeze your own urine as well.
