A modular rack system, for adjustably attaching equipment to a vehicle, includes a base mountable on a side wall of the vehicle. The rack system has a first wall that is disposed on and upwardly emanating from the top surface of the base that defines a lower seat. One end of a vertical member resides in the lower seat and is secured thereto. The other end of the vertical member resides in an upper seat defining by a downwardly depending wall from a saddle and is secured thereto. The first and second walls laterally stabilize the vertical member relative to the base and saddle to permit the base to be mounted to a side wall of a vehicle and a top rail to be secured to the saddle without the use of gussets or cross-braces.