I use a pet taxi. It's about 2x3 like the others use. I prefer the plastic, becasue I feel it's more den like. I also like being able to wipe it clean, it's lightweight and I can put it in the car and run a seatbelt thru the handle and buckle them in. It kind of looks thike the one in this link
http://www.petmate.com/Catalog.plx?CID=8