Hey 10G. I'm just back from a trip over the Simpson - up to Darwin - and across the Gulf back to Brisbane. Around 12000km. I had a single plastic 20L jerry on the roof, one of those yellow ones from BCF.
It was mostly empty, except when very remote as an emergency source.
At first I had it up-right - spouts skyward. But then I carried it on it's back with the spout down closest to rack. I simply used 2 ratchet straps to hold it down on my Rhino Pioneer platform via eye-bolts. I did up the main and breather just by hand. Never had a drop come out of either.
It makes a surprsingly big difference to fuel economy to have it standing up!

Quote Originally Posted by 10G View Post
Thanks for the experience guys. Did you guys run the Jerrys standing up normally, or on their backs (I guess it's the back) with the breather outlet facing down and the main outlet facing the sky?

That's how I'm hoping to mount them.