Then I have the perfect solution (albeit, a temporary one)
Go to your local hardware store and buy an expandable shower curtain rod. Not the spring-loaded one, but one of those that you screw out. They have a rubber foot on each end and use friction to mount securely to your shower walls. The more you screw the two halves out, the tighter it gets.
Unless you are going off-road or over some really rough roads, I think it would hold a camera body and a reasonable lens.
Now all you have to do is figure out a way to attach a mount to the bar. If you have a tripod head, I would be willing to bet you could find a clamp at your local hardware store (do the Aussies call them ironmongers like the Brits?) that will let you attach it..... A clamshell conduit clamp of the proper diameter would probably work. Then chose a bolt to attach the two halves of the clamp, and make sure it is the right thread for your tripod mounting screw on the bottom of the camera.
Makeshift, but I think you could do it with a little effort.