spi epoxy barry company owner highly recomends as a chassis and component coating. he tested its durability by submurging it in brake fluid for 30 days and still had no wrinkling or softening. it will seal against moisture. rust is like fire if it has one of its 3 components taken away it will not continue to grow. cant take the iron out but can remove moisture and o2. easy to apply sprayed or brushed. you can even scuff and recoat if you do scar it reassembling your rig. i highly recomend it. go onto hotrodders.com and search spi or go to their forum site and search or ask questions. even in the paint and body section of this site has good articles about spi. i am not associated with them at all but am a firm believer. it is inexpensive also
http://www.southernpolyurethanes.com/Pricing%20Info.htm less than $150 for 2 sprayable gallons twice what you need for frame only.