I have worked with the same problem. I took my pressure washer and put on the pencile tip and sprayed it in the hard to get to places and knocked everything loose out. Then I used Zero Rust's Prep step in the area then Zero Rust Paint. I thined the paint down little more so it will get into the tight areas. I primed the entire cab to my truck with it. Its been sitting out side pretty much uncovered since about May. Havent had any rust come back. Here is their web site.
<a href="http://www.zerorust.com" target="_blank">www.zerorust.com</a>