I do not know the best solution, in any case, here is what we did:
RustbulletAutomotive from Rustbullet.com.
This product is the best I have found for rustproofing seams and crevices.
Developed for our military, we literally hand brushed this silver colored product in every nook and cranny on our 68 Camaro. We even used mirrors to brush hidden places.
Before I applied this product to anything, I did a rusty test piece and threw it in the back field for a full year. My test piece never rusted or pealed or even faded.
If interested, check out the reviews on their website.
Hope this helps. Again, great question! Keep'em coming!