A mobile storage unit for a mobile storage system includes a pair of axially extending wheel units, each of which defines spaced apart end areas and includes a wheel arrangement. A storage unit support structure is interconnected with the wheel units, and includes upright support members and shelf support members. A pair of upright support members are engaged with and supported by the end areas of each wheel unit. A lowermost shelf support member is secured to an end area of one of the wheel units. The lowermost shelf support members are secured to the upright support members and to the end areas of the wheel units. Each end area of each wheel unit includes an upwardly facing engagement surface, and the lowermost shelf support member is secured to the upwardly facing engagement surface. The upright support members are also supported by the upwardly facing engagement surface.