For rack mounting this is the best solution IMO. I came across a rover on the trail last weekend with one of these and asked him where he got it. He gave me this website:
http://www.roveraccessories.com/fuelstorage.htm
Cost is $75 for the single and $135 for the double.
Nice thing is, they lock. Both the Nato and Sceptor cans fit.
Only drawback is having the empty mount bolted to your rack when you not off-roading. The other thing is - I bought the last double they had and I got the impression it was the last one ever since they are now just bolting singles together for multiple cans.