I feel your pain, i am counting down to my Fraser Trip. I am heading over for 10days starting Nov 20.
You can book up to 3months in advance but no ealier (for camp sites).
I am heading over with my family and another family, all in total, 4 adults, 2 kids (both 7yrs old), and 3 under the age of 2 ( a 2yr old, a 10 month and a 7 month old)
We will be camping at Dundaburra camp ground.
I have been over several times during the long weekend periods (Australia day, and may day) and never again. Too busy for my liking and unfortunitly the " insert word here " come out to play also.
I hate to admit it, but alot of people think they'll be right and take no recovery equiment or shovel.
You can book everything through the barge (manta Ray) http://www.fraserislandbarge.com.au/
Tide time tablehttp://www.bom.gov.au/oceanography/tides/MAPS/qld.shtml
And the NPWS web link (they have fortnightly island updates)http://www.derm.qld.gov.au/parks/fraser/index.html
Hope this helps