At GMH, call ATC on 118.1, the eastern frequency. GMH can be difficult to identify. It is an old industrial complex with a dark, sawtooth roof, approx. 7 nm east of Moorabbin and just south of the junction of the Monash and South Gippsland freeways.
For approaches to RWY 31R, 35R or a downwind join to RWY 13L, you will often be requested to report at Parkmore Shopping Centre and/or crossing Springvale Road (a major north-south road), which is just inside the 3 nm CTR boundary. Approaches to RWY 17L will often track via Sandown Racecourse to join a left base.