This might be getting into "Which brand of oil..."
Bruce Palmer recommends Kreem or POR 15. Others say Red-Kote. I wasn't aware of KBS until now. Looking at their
website, their 3-step kit sounds just like POR's 3-step kit. And their sealer is the same color as POR's. I suspect all these brands use very similar formulations. The 3-step kits have a "cleaner" to remove dried-up sludge and gunk, a phosphoric acid-based etch to remove rust, and a sealer "paint" that is formulated to resist gasoline.
No one can guarantee that their product is everything-
proof. They can advertise their product is most-things-
resistant. Take a look at the long list of gasoline additives listed on
Wikipedia. There are probably others in use today, and new ones will show up in the future. And if like Hayley, you get gas that is 40% alcohol with god-only-knows what else in it, you are likely to have problems. Nothing is god-only-knows-what-proof.
I really think preparation is the key to success - not which product you use. My KH tank was very rusty, and had a lot of dried sludge on the bottom. I used drywall screws and a lot of shaking, which got most of the rust out, but not the sludge (next time I'll use fish-tank gravel). The POR-kit's cleaner got most of the sludge out, but not all. I had to manually scrape the dried sludge to break it up enough so that the cleaner could penetrate it. This is difficult due to the shape of the tank. After several days of scraping and soaking, the sludge was gone, and I was finally happy with the result.
Getting out the dried-up gasoline sludge is the hardest part. I didn't try solvents such as acetone or MEK (methyl ethyl ketone), but these might help. I'd stay away from muriatic acid or lye, since the metal is already getting thinner on these old rusty tanks - we want to dissolve the sludge, not the tank.
The phosphoric acid etch quickly got rid of the rest of the rust. No problems there.
Completely drying the inside of the tank was difficult. I used a heat gun stuck in the filler opening. One would think that 15 minutes of full-blast heat gun would dry it completely, but it took much longer. Hard to see in there, but I found little wet spots in the corners. I rotated the tank to different positions so the water wouldn't puddle in one spot or another. When I was finally convinced that it was completely dry, I poured in the sealer and rotated. This part went smoothly. Best to do the sealer as soon as possible after drying (and letting the tank cool) so that surface rust doesn't develop.
The sealer forms a pretty thick coat - you definitely want to make sure it does not get in the petcock threads or any other openings, as it is thick and tough, and you'll have difficulty screwing the petcock in if you get it on the threads. You need to put something (like a nail) in the crossover fittings so they don't get clogged.
The finished product is only as good as the prep work.