03 QX4.

I'm looking at doing the White Rim Road in the Datsun in a couple of months. I did a chunk of it last year and using some creative math I'm guesstimating 7.5MPG for that portion. Along with the pavement portion I'm looking at 130 miles, which should be doable on a full tank. But I'd like a cushion, which means extra gas. On the roof is the only realistic place, I don't want the possibility of a leaking gas can inside the truck especially in 100+F temps. Since it's in the middle of a 4K mile vacation, off the trailer hitch isn't a good option either.

So, any suggestions, do's or don'ts for carrying extra gas on the roof? Either carrying it in general or specific containers.

I can't imagine any reason you shouldn't, with the exception of the obvious safety issues.

Off-roaders use jerrycans on the roof rack all the time, or hanging off the rear bumper.

My larger concern would be the movement of fuel in a half-filled container at speed. A well-sealed container designed for external carrying should be fine. If you use it, use the whole container, because you don't want 40 lbs of fuel sloshing sideways 8' off the ground.

Thanks, but I actually meant the nuts and bolts of it. Like is there a ideal container where you go, this is just what it should be... A particular way of mounting it to the crossbars, or is a box better, or a platform or whatever? It's going to be 3K into a 4K vacation and even the empty(s) will normally have to be carried on the roof. Just strap it on but how to stay low profile and not have lots of extra wind noise/resistance?

That's probably a better question for off-roaders. A jerrycan is a thing, you can look it up.

How to put a big container on the roof and not have lots of wind resistance? You won't. I mean, look at the rigs that do long rallies.
https://www.equipt1.com/products/jerry-can-mount

Here's a great place to ask: https://www.nissan4wheelers.com/