hey
i have been using KBS on my car
and i think it is really good stuff
and they have a kit for the petrol tank
http://www.kbs-coatings.com.au/Auto-Fuel-Tank-Sealer-Kit_p_15.html
and the is also instruction videos on how to use it
http://www.kbs-coatings.com.au/KBS-Instructional-Videos_ep_76-1.html
so atleast this is another option