Silly me, it was on your post.

The car is electrocoated, but there is no galvanization.

When you paint, you want to make sure you do not disturb the first primer on the car if at all possible. That is the electrocoat or e-coat. That is the key to corrosion resistance on modern cars. It was a PPG invention, and those were the most valuable patents ever to exist in the paint industry. PPG cationic e-coat had a 96% market penetration at its height--the same as Windows on a PC. There is no refinish substitute for e-coat for corrosion protection.

When you prepare the surface. Try not to disturb the ecoat. Rust will increase dramatically if you do. Also, there are some very toxic heavy metals like lead in the ecoat. You do not want to breathe those in.

One thing that a lot of people make the mistake is sanding and prepping the car and leaving it outside. Big, big mistake. Ecoat cannot tolerate any UV. None at all. Not even a couple of hours. E-coat manufacturers have very stringent UV transmission standards for topcoats. Maximum allowable UV transmittance specs are written into the contract. If there is delamination of a coating off of e-coat, the first test the e-coat manufacturer does is a UV transmission test on the topcoat. If that fails (too much UV goes through the topcoat), then the e-coat's warrenty is voided, and the auto company is responsible for the failure. I've seen e-coated car bodies left out by the manfuacturer chaulk in 8 hours in the sun.

The only way you can fix UV damaged e-coat is to remove it. Sometimes you have to remove all of it.

I've found the most successful repaints disturb the original coatings as little as possible.