Rust on 2007 Tacoma

This weekend, I noticed a small pencil-point paint chip on the very edge of the driver's side door that appeared to be showing rust underneath. It's only noticeable if you're really looking over the truck with a fine tooth comb, but I'd like to deal with the situation right away.

I'll be taking my truck for an oil change/quick inspection at the end of this week, as it's just before the 3,000-mile Toyota Certified Used Comprehensive Warranty runs out (I bought this 2007 used a couple of months ago). I'll show them the speck of rust on the door and it'll be dealt with then, hopefully.

Is there anything that I should be aware of as far as warranty limitations (used 3,000 mile warranty is up in another few hundred miles, but the PowerTrain warranty will be in effect for a long long time...but I'm assuming the 100,000-mile warranty doesn't comprehensively cover rust issues.) for future rust issues if there are any? What are the best methods to counter the rust problem in the future?

Thanks, y'all.