TBH I never lined this tank: http://motorbicycling.com/f26/diy-ta...ant-17323.html
and ofc the stock ones aren't lined either & as I use them frequently the fuel/oil mix keeps them completely corrosion free... So, if yer tryin' to save a few bucks on a bike yer gonna use ya can skip lining 'em and just check them frm time to time.
I figure if rust ever does start to become a problem I'll clean it then *shrug* I will say if I were to build a show bike that sat most of the time I would most likely line the tank as an unlined, dry steel tank would no doubt rust w/a quickness
For storage of a dry, unlined tank, ofc ya can jus' hit the inside w/some WD40 or w/e...