Since my ol' lady and I were riding 2 up in some fairly remote areas, I was looking for a gas can that fit the saddle bag. Now that we ride separate bikes, doubly so. I found that the Wavian 10 liter fuel can fits, without modification to the tank or the bag. the only "downside" is that the can doesn't fit fully into the back half of the bag due to the bag latch mech. So behind the can are my air pump, tire plug kit, small ratchet set, and some rok straps. The tank seals well and I have not noticed any fuel smell when I open the bag. I also ended up putting the tank in the opposite direction that it is in in the pic, so that the cap is uphill when mounted on the bike.
 
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That is a pretty neat and tight fit!

I use one of the tractor manual holders mounted under the left bag and a MSR fuel bottle.

Hit the red fuel light a few years ago in Wyoming (never assume a marina will have gas) and had to beg a camper for some gas out of his boat to make it back to civilization.

I use one of the tractor manual holders mounted under the left bag and a MSR fuel bottle.

Hit the red fuel light a few years ago in Wyoming (never assume a marina will have gas) and had to beg a camper for some gas out of his boat to make it back to civilization.

Last summer, we had 6 bikes on a trip and we had a few detours that took us away from normal gas stops. I knew there was a gas stop at Detroit Lake in Oregon which we were riding around, so no big deal.
Until we passed the gas station and the concrete pads around the pumps had been removed down to the dirt (a foot drop or so). So, no gas.
Three of us were on fumes when we finally got to Sisters Oregon (57 miles), but we all made it. Luckily it was all downhill from the lake to Sisters.

We did have a buddy in his Porsche with us (he had shoulder surgery and was not cleared to ride yet), so he could have gone ahead and bought a gas tank and topped us off if needed.

UPDATE TIME!

I have had to order a new tank. The most bizarre thing happened. The rivet that holds the elastic retainer in the saddlebag, has worn through the bottom of the gas can. Found gas dripping out of my saddlebag. I think I've come up with a mounting solution and I'm going to make that bag my permanent extra gas can holder.

Try cutting up an old car floor mat to cushion the tank

I got some EVA foam and I'm going to put some lashing straps in there too.