I will start with probably a silly question - can you get bike racks fitted to a 17.56-2 Expanda? Or is this not possible because of the rear bed? And if it's not possible, what's the next best suggestion please! 
Matty can you tell me how you got your storage box on there with your gas bottles?
This is how I transport bikes on mine.
It's made by
http://www.tradesmantrailers.com.au/Bike Rax/more_information.htm