Rectangular ones still kinda look gun-ish. I know you're not supposed to have airsoft or paintball stuff on the buses in KW, so here having a guitar case that could easily be mistaken for a gun case on the route that passes the field might not be best. Probably the same case there.
I would just buy a big regular guitar-shaped one and cut foam to put stuff in safely and securely.
Hockey bags are also a good idea, although you couldn't mix the two. Latency had a great point with the amp bag for the rest of the gear. I'm going to look into that for myself actually...