I have mine in a hardshell case it works fine and is on wheels!!!
If you are flying I would say you definitely need a hard case and I would recomend talking to the airline before you travel and explaining to them what you are carrying. I did this both times I have flown and have had almost no problems- When I arrived at Check-in they labled my case as Fragile and then I had to check it in a special dept where they take greater care- I also advised them that I had a 'Toy' gun, I was advised not to use words like replica, security asked me to open my case so they could see and after they got excited at what they saw they allowed the baggage through and sealed it with a secuirity tag so that it wouldn't be re-inspected. It is also a good idea to carry a pic of yourself in costume with and without lid so they can see exactly what you do. I carried my lid on as hand-luggage and that wasn't an issue although you do get some looks when it goes through the xray!!!