How did you rustproof your bottom?

In my opinion NOTHING beats POR 15. Not a one step process to do it right ( cleaner, neutralizer, two coats POR 15, top coat when tacky so no need to rough up like previous poster mentioned) but you will NEVER have to worry about it again. I also use it on boat trailers that have sat outside year round for 8 years, besides going in and out of water, and they look like they were done yesterday.