The gas tank sealer would be the best product for this. It absolutely will not peel. See our testimonials page at
http://www.caswellplating.com/testimonials.htm where you'll find at least 5 testimonials about our gas tank sealer.
We don't sell a tin plating kit at all, and even if we did, getting any electroplate inside the tank would be extremely difficult.
The only possible solution would be electroless nickel, but the problem then becomes adhesion. The inside of your tank would have to be 100% oil free for the plate to stick. You'll have to get a plating bath big enough to immerse the entire tank.