I was lucky last year and found a Tiregate HG Series hitch mounted tire holder for about half the MSRP on Craigslist. The owner wasn't happy with it because it holds the tire a fair distance off the rear end of the vehicle.
Wilco, the makers of Tiregate, make a jerry can holder for my device, but I have two problems with it. Firstly, it holds the cans very high and I wouldn't be able to open the rear window with cans that far in the air. Secondly, it costs $330 USD. Here's what their device looks like.
I decided to see if I could make my own alternative. I bought two jerry can holders on Amazon for $35 each and realized that I could mount them to the tiregate pretty easily. I went to Home Depot and bought several feet of 2"x3/8" steel bar, drilled and hole-dozed it to fit the 1" tiregate mounts, and mounted the jerry can holders directly to that. Another steel bar runs across the lower section and is bolted to the tiregate to ensure that the cans don't sway. It is primed and painted so it shouldn't rust.
The jerry cans sit about 1" off the gate of the truck and about 1" on top of the bumper step. I can open the back window without issues.
I know ... most people use the red cans for standard unleaded. Red cans were available, but they were horribly rated so I went with the user-rated green cans by another manufacturer that were available.