http://www.ion-products.com/water/men/travelgear/kite-boardbags/gearbag-13-golf/I've traveled with this bag and it's awesome, can fit 3 to 4 kites + harness + 1 board + 2 bars and a few clothes just around 23 kg. The wheels and frame make it easy to carry over short-medium distances.
Cocos Flights from Perth are roughly $500 one way (more or less $50) and include 1x 23 kg check-in baggage. If you're afraid of being over or just want to bring more gear, just pre-pay an extra 23kg bag for $55 (each way). I double checked with Virgin yesterday and even for Cocos there doesn't seem to be any worries for having up to 3 x 23 kg checked in baggage!
Just make sure you're not over 23kg, virgin started to be pretty specific with this rule over the last year or so. They won't let you check-in even if you have 1kg over (unless you pay of course $30 per KG from memory)! Last time I had to wear my harness on the plane as I was 2kg over

I could be wrong but Virgin doesn't seem to have any restriction with size or length of checked-in baggage, just weight limits. I traveled with Virgin all the time always with oversize baggage and never had an issue with size or length.