You used to be able to get RotopaX defects for cheap, but that looks like a thing of the past. They also have RollpaX that you could likely find a way to mount/use.
https://rotopax.com/products/rollpax

I still think that the larger tank is easiest. You don't have to fill it if you don't want the weight or need the mileage.

MSR fuel bottles are cheap and easily mountable/removable too.

 

Thanks Bmart and Tacoma. I currently carry a 1-quart fuel bottle in a tail-mounted box; so far I haven't had to use it. In a month or two, prior to my next BDR, I will decide whether to go with the Rotopax or a larger main fuel tank. Thanks for all the suggestions.
Will