I find that the rule with ferrets in cold conditions is: give 'em *lots* of
extra towels, rags, old blankets, whatever to burrow into and they *will*
make excellent use of it all.
 
In a *worst* case scenario, like an unheated room for long periods barely
above freezing, consider trying to actually create a homemade rabbit burrow?
Something like a smaller padded box buried deep in a pile of blankets in a
larger box with a PVC pipe leading down to the smaller chamber?  You'd have
to make sure the entrance couldn't get plugged up with blanket or whatever,
it'd be an interesting engineering excercise.
 
What I use as *my* blanket is an old "mummy type" sleeping bag where the
last 1.5 feet is tube-shaped.  That tubular thingy hangs down over the
bottom of the bed and the ferts slide past my feet down into their "hammock"
so I spend all night automatically pulling my covers back up 'cause there's
almost five pounds of weasel trying to drag them off.  The guys spend all
night going slooooowly up and down about half a foot.
[Posted in FML issue 1732]