gday mate, not sure on directions but i can tell you its really eroded at the moment.
Here is a vid of me doing it a couple months ago with some mates.
If you watch it from the start you may get an idea of how to get thr, the fun starts at about part two or three i think.
Massive amounts of damage on all trucks. Not recomended if you like straight panels at all. Fun track though.
No sign to the track either, nor for any of the tracks in GHM, are you sure your thinking of the right spot? i live just up the road from GHM and get out every few weeks and have never seen a sign.