I agree with the other members. Most carpets definitely appreciate vertical climbing space. They're also much too nice of a display snake to be kept in racks IMO. They can obviously survive in a rack system but you'll miss out on a lot of their natural behavior and beauty.
@ M.P.C.- I was a bit intimidated and misinformed about the husbandry needs of carpets too. After talking to some experienced keepers and doing LOTS of research I took the leap. Caring for them really is a breeze. Not much different than my colubrids. I just keep the carpets a little warmer and give them more climbing branches.