A mounting pad system and method for an HVAC outdoor unit that includes providing a lightweight fillable pad shell containing a gelling material and having securing slots extending from an underside surface to an upper side surface of the shell. The shell is filled with water through a port at its upper surface. Prior to leveling the filled pad on the soil at the site and installation of the outdoor unit, securing straps are inserted into the slots from the underside surface of the shell so as to extend through an upper surface thereof. The filling port is covered when the HVAC unit is placed on top of the pad. One or more securing anchors can be used to anchor the pad to the ground, which are also covered when the HVAC unit is place on top of the pad and an anti-theft cable can be employed to further prevent theft.