Carrying gas for generator

We have an Alp Adventurer TC on a 2015 Chevy Silverado Dually. We do a fair bit of boondocking as well as camping in campgrounds that have no AC hookup. So, we purchased a Honda EU2000i. What do you think is the best way to carry spare gas for that generator. I've been thinking about purchasing one of those diamond plate metal boxes (if I could find one), bolting it to the top of the rear overhang of the camper, drilling some vent holes in it, and using it to store one of those approved polyethylene gas containers ... maybe 5 gallons. Don't much like the idea of just the plastic container sitting on the back of the camper, so I figured the metal container would afford some extra protection. Then I thought maybe I could use one of those low profile RotopaX containers (3 gallons?) and attach it to the rear overhang ... maybe behind the ladder. Some of you must have had this problem before and I was wondering how you handled it?
I searched the forums, but couldn't find anything. Maybe I didn't use the right search parameters. By the way, if I have this post in the wrong place, I apologize and feel free to move it. Thanks.