Why don't you clean the rust off, and paint it with epoxy primer,??. That would be the best rust protection. You can grind it off, or sand it off, or sand blast it off.
That is what I would do.
As far as seem sealer I would use "Lord Fusor" 803. It's tuff and sticks to any thing, and you can paint it in 10-30 mins.
Just my .02
barracudadave67