Any case will do if it hides your airsoft and if it it protects it from other gear. I use a plastic CanTire case for my sniper. A Condor gun bag for my M4, mags and bb's etc go into the pockets. My PDW is small enough to go into a CanTire technician case (briefcase) and you could play soccer with that case without harming the PDW
Rest of my stuff go into my backack or a temporay plastic bin.