Seeing how weak the stock tank is made me set out an alternative.
I saw some rear rack mounted keg style tanks I liked and scavenged for some material. A 7" length of 6" round pipe with plate welded for end caps and a custom cap.
Here it is all welded up, still gotta do some grinding and treat the inside and paint of course.
I calculated it to be roughly 0.6 US Gal.