IMHO, tink watever material they use to make the petrol tank, it shd b able to prevent oxidization or deterioration, and under warranty. Dont tink by leaving ur tank on low volume will cause oxidization inside/or outside, even if u din drive for sometime. It ll be a big worldwide recall if this problem happen. Based on current technology available, this is not a problem to them anymore. So dont worry about this issue. Cheers !