I keep mentally chewing on the military aspect. Irwin Barracks is straight across the railway line from Karrakatta Cemetery, is walking distance to the pubs, and is adjacent to the quite secluded Shenton Bushland. On Google maps there is what looks like a white station wagon parked at the security office on Stubbs, and on Street View there are white vans at the gate. In 1996 what is now the Stubbs main entrance was a little used wire mesh gate that from memory was usually unattended, as the main gate was further south in the area where the new residential subdivision is now. I think. Very quiet. You could come and go and no one would ever notice.
Campbell barracks is a short drive away, is walking distance from where Julie Cutlers car was found, and in between there and Claremont is Lake Claremont. If you were in a big hurry to dump a body late at night that would be a fairly dark and quiet place to leave it if you didn't want to do the Shenton Bushland thing from Irwin. Concealment in the reeds would be fairly simple for a soldier.
A funny thing about military bases is that there is usually very little movement at night, and when there is people don't often ask questions or approach others. The military also doesn't try too hard to cooperate with civilian police. The officers give it lip service, but the men see civilian police as the enemy, and are usually totally uncooperative without making it seem obvious. That was my personal experience, anyway.
As for the southern dump site, when I regularly traveled to the Rockingham/HMAS Stirling area from Claremont/Nedlands in 1996-99 I used the freeway and got off at Thomas Road, and went the back way through Baldivis. Straight past Millar Road. Why the freeway? The Fremantle traffic police made Cockburn, Rockingham, and Stock Roads a nightmare, and you had an excellent chance of getting pulled over or getting photographed by a Multanova. There was never a weekday daytime RBT on the Kwinana Freeway that I ever saw. Weekends at night there was often an RBT in Como, or the other site near South Street. You would have a real chance of getting pulled over at night on the freeway on the weekend. That makes me think that the body was transported and dumped during daylight, not at night. But where do you keep the victim concealed in the meantime (probably not in a station wagon), and who doesn't require you to account for the mileage for the trips to the dump sites if it is a pool car, or you are working in the area?
The Millar Road area is interesting. That was fairly hard to get to back then, and there wasn't much going on in the area. Dumping a body would have actually been quite risky, as it was a long drive from Claremont, and there would have been a risk of being surprised by horse riders. Especially on weekends, and early in the morning. That is an odd area for someone to be intimately acquainted with, as I always saw it as somewhere unpleasant to drive through on the way to somewhere better. It is also not far from where Gerard Ross was found. You would have to make quite an effort to drive to and scout that area, unless the killer just tossed the body and ran, but I believe the body was concealed (?), so he took his time at the site. Ballsy. Or was he in a commercial vehicle in broad daylight, ladders on the roof, and clipboard in hand. Puzzling. The area back then was a deserted hell hole of scrub and back roads that seemed to go no where. How would he even know how to get there..?
Pipidinny Road is on the way from Irwin/Campbell to the Lancelin Defence Training Area, and you would probably drive past it if driving to or from RAAF Pearce from Lancelin. The SAS trains at Pearce. They have a mock up airliner that they like to play with, and they like to jump out of planes.
A local military guy would also be known to appear and disappear from the pubs on a regular basis, but people probably wouldn't notice if he wasn't around for a while, or was on his own 'meeting someone'. He could be 'known', but without people really knowing much about him, and would have a perfect excuse not to say what he had been up to. In between attacks he would presumably want to stay right out of the area, and then move back in some time later.