[Foot Stomper]

I won't comment on SPI because I don't pretend to know their products specifically.

Sealer? I recommend reading the TDS for the paint you are using as it will give you the correct procedure. I would not rely on any primer manufacturer for paint application and prep instructions.

You should paint the pieces hung like they would be if they were on the vehicle. Another way to do this is to paint the edges and hard to reach areas, then install them on the truck and paint the entire vehicle. Pros and cons to both methods.