what r u guys using to store wheels safely so they dont get marred and hammered when not at the track or in transit??

i have a pit cart that holds 4 wheels when at the track, but just curious if there are other portable, "wheel only" carts to storing a host of wheels when in storage or at the warehouse? something portable with wheels would be really cool.

between the couple of race car and spare wheels, i got wheels leaned up against the wheel everwhere.