G'day Todd,
Probably a bit late 2 help with your packing goals, nevertheless, I have been xperimenting with different ideas with a mind to getting 2 Toowoomba (that didn't eventuate). However, I'm still brainstorming and I came across these Tactix Technician's Case on special one-off sale at Bunnings NSW at this time. They r $39 each and could b easily waterproofed using adhesive weatherstrip (like the stuff used to keep out draughts in doorways). Anyone interested can investigate further by asking at Bunnings for item code BUN-320064.
With 2 cases, tied on roughly, the cases are in an ideal position 2 provide good back support. I rode home this way from Bunnings and with small adjustments and a cushion, this could work really well:
Here, 1 case is used as back support and other items like large tent, table etc can b tied on securely:
Finally, with careful and judicious packing, the second case (on top) could b used for light items like clothing, towels, pillows etc. The problem with wide loads and mirror obstruction is a serious 1 and I have solved it by installing xtra mirrors on Ram mounts high and wide (from Adventuremoto.com.au):
Anyway, some packing ideas 4 OzSToCobbers to consider.