I may post this on any other thread about carrying fuel, but I'll start here on the Tool Tube discussion. A few years ago, I followed this thread and added two tool tubes to my TW rack for carrying spare fuel:
This worked fine for a few years. However, during March Moto Madness in Tennessee this year, we had to run a few miles on the WORST pot-holed gravel road I've ever seen. The plastic tabs on the tool tubes just didn't survive. I made it back with liberal use of Gorilla tape! When I got home, I went to work on "fuel bottle V2.0" and scrapped the Tool Tubes altogether. I bought two fire extinguisher mounts that are hard-bolted to the rack. I then use these handy Titan rubber straps to secure the tank. I'll be riding in the Michigan Upper Peninsula this weekend to give them a pounding. I hope they survive.