I did an 86 FZ750 that way, stripped the steel tank down to bare metal, polished the heck out of it. Then cleared it. I used a good fast 2 part urethane clear coat, and never had any problems. Rode the bike for 6 years, sold it, repainted it for the new owner and it was JUST starting to get little tiny rust spiders showing by the rear tank mounting bolt...
The trick is if you do polish it, you have to CLEAN the tank with prepsol to get all the polish off before clearing it. But you need to clearcoat it RIGHT AWAY! Don't give it time to oxidize. Plus if your tank isn't perfect...you can't use filler on a bare metal tank or you'll see it obviously.