Hi Guys
I have just come off Fraser Island at the beginning of January. You may wish to check out with the locals which camping areas are closed due to Dingoes. there were 3 or 4 areas closed while we were there due to aggressive behaviours (from the dogs... not the people).
Barges -
I used the Mantaray barge at Inskip Point. You can get a return ticket which works out a bit cheaper. You can purchase those at the national parks place just before you enter Rainbow Beach. It also allows you to get a fuel discount at the servo in town. It was 8c a litre discount in January. They can supply you witha current beach/water/track/dingo/crocodile condition report as well, which I found really useful. And a current tide chart to avoid being stuck trying to get off the island at high tide
Frasers at Cathedral is a far cry from your standard Big4. But the pub next door is very good with lots of backpackers to make it interesting.