You need to keep a very close eye on yourbunny(ies?), to make sure there's no chewing and eating of carpet orother materials that could cause a blockage.
I'm finding that gras mats over plastic office mats + a canvas tarpworks well, but that's just me. If you look at the NIC cage thread inthe Photo Philes forum, you can see what other people use. Definitelyworth a look, for ideas, etc.