hmm. ??? I wonder if your vet meant covering the entire condo, sides and all, completely with a sheet… I could see how that to hinder air flow. My condo top isn’t covered all the time and D isn’t in it all day. The condo will also have to be redone once my rabbits have formed a trio.
Since I’m talking condo…. — A word about the tiles I’m using on the second floor; they are very heavy, rough surface tiles that sit on card board squares underneath. I tried using carpeting but Deirdra is a determined carpet-digger/ripper. She did’t like blankies up there either but seems to love the coolness of these tiles (Deirdra seems to feel hot a lot). Since the weight of a tile plus Deirdra’s poundage adds up to about 17 lbs, the shelves sit on support grids in the middle which form the tunnels underneath.

Above is the L-shaped tunnel
this is the straight tunnel, with D’s box (Mops designed for her
)