I usually head out to the state forest on the eastern side of Mundaring weir, there's a belt of pine plantations that follow the length of the weir and last year some where harvested leaving large clearings from the surrounding Jarrah and Wandoo forest, great spots for setting up and pretty dark to depending on how far south you go. Access is a little tricky which is probably a deterrent to the "bad elements" but worth it to try considering the relativity closeness to the city {Ive read on some WA 4WDriving forums the state government is going to put further access restrictions on this area being a water catchment area
}.Google earth pic attached