I've got clear shower curtains stapled to the front of the hutch, but mine are roof opening - you could fit elasitc in the shower curtain holes and loop it over hooks on the hutch, if you wanted to fold it down to open the hutch.
I just put a couple of big rugs on top of that, totally covering the hutch - tried duvets and the water still froze - carpets are great, especially the gel or rubber backed ones, as they keep the hutch dry and insulate it too - I use nursery fireguards and bricks to hold it all down - from Argos. Take it all off in the day even if it's freezing (except for the shower curtain) - as the barmy bunnies choose to sit in their run whatever the weather :roll:
Maa insists on sitting in her run at night too - I guess cold means nothing to her, or maybe she sneaks upstairs to her cosy hutch at midnight?