I'm pretty sure this has been talked about before.
A thread over on ADV sparked my interest.

http://www.turtlepac.com/sportdetails.htm

The 20 litre one at the bottom seems the go.

I like the way it rolls up when not in use and they are supposed to be very tough.

Here's a link to the thread as I imagine there will be all sorts of options and opinions posted.

http://www.advrider.com/forums/showthread.php?t=497356

 

5.3 gallons? Bwaahaha! Well I gues you wouldn't have to fill it all the way. I really like the idea of a bladder though.

 

Yeh 20 litres is alot.
Maybe these 8, 10, 12 and 15 litres.

http://www.liquidcontainment.com.au/fuel_bladders.html

 

Hi Guys - question - how would you attach this to the bike? I do not see one staying on the back rack with bungy cords when riding in the bush, desert, etc. Then, it would take up the whole rack. I do not think that I would want to hang it off the left hand side of the rear of the bike.

 

Check out the ADVRider site.
There is sooo much info on this and many other aux fuel options.

 

Good idea but it does seem a little awkward....

 

So my hard cans in the aluminum holders that I have are more or less dangerous that rubber? LOL