Rust proof my car? How?

I start noticing little sport of rust around door edges, especially at places very close to the road ( where sheet of metal bended ) and trunk door has rusting bubbles . Some places around wheels has rust bubbles as well.

So question is how I can stop, slowdown rusting process of doors and under the car? Can I use some kinda coating over door paint around dor edges? Is there anything that will create some kinda layer which when dry will be flexible but protect doors from rusting even more?