Roger, with the new 80 channel UHF CB gear you should have no issues finding a free channel. They use standard frequencies so any brand will talk to any other brand.
Just stay from the emergency 5/35 and other "well known" ones like 39 and 40.
http://www.uhfcb.com.au/80-Channel-UHF-Information.php
Pick a free "Simplex" channel since you probably won't have a duplex repeater in the area, and that would get you other traffic. You could have an open access channel and let individuals pick their own private channels.