Wheels are very useful, but one of those cheap and cheerful fold up luggage trollies will add them to a case very easily. We always carry a bands instruments for them, and a 120 bass box in case is not light. Wheels are great.

Swan ( www.swanflight.com) are the the company I've seen used the most. They will manafacture cases with wheels on request. Our dance societies PA is in them, and has suvived more flights, joureneys and general banging about than I care to think about without any problems