I have a Thule luggage carrier, which has more than enough room for 4 snowboards and all the gear that goes with it. Keeping everything inside a carrier like this keeps the road grime from getting into the bindings, keeps road salt off of the edges, and just keeps everything much cleaner in general. Personally, I think it's a better way to go.
http://www.thuleracks.com/thule/prod..._id=11&sku=683