Well, I can't help with the gas-carrying laws in Alaska, but I endorse your plan to cover the can with cordura instead of that, um, festive material.
But I have to ask, where in Alaska are you riding where you feel the need to carry 3 extra gallons of gas? It's only 244 miles from Coldfoot to Deadhorse, and I don't know of any longer on-road distances between gas stations in that state. Seems like the one Rotopax should do the trick.
I'm tryin' ta think, but nuttin' happens!