Rust around ground studs in sheet metal

[APC9199]

I am fabricating some sheet metal components out of 11ga (.120") 1008 mild steel. They get self-clinching stainless steel ground studs installed into them (PEM FHS-M5-15). Traditionally we have used Picklex to prep the sheet metal components for powdercoat followed by drying with a blow gun, then use localized zinc (plug n' plate kit) around the ground studs to prevent corrosion after powdercoat. The parts are pre-baked to drive any moisture out of them from the prep steps, then powdercoated. The problem we keep running into is corrosion around the ground studs after transit to customer locations...sometimes in places like Singapore or Malaysia. We suspect that the plating solution is wicking into the seam around the hardware and not coming out when we blow the parts off and bake them. It is then dried in place and shipped to these humid locations where the solution "activates" and causes rust. We are transitioning to iron phosphate as an alternative prep for powdercoat, so we are going to try that in place of the Picklex to see if it performs better. I am preemptively asking on this forum to see if anyone else has dealt with a similar problem and found a reliable solution? This type of sheet metal design is in use around the world and clearly not everyone has trouble with this.

A reference for the installation method for PEM studs...


An example of the situation we are dealing with...