I've elected to prime the interior parts. I'm using SEM Self Etching Primer and the purple Harbor Freight HVLP Spray Gun. I found a very good YouTube video on how to set up and clean the spray gun. The tip is VERY hard to remove the first time. Almost like it was not intended to be removed. I was able to order the SEM Primer by the quart and used a Mixing Mate Paint Lid I found on Amazon. Some small parts I used SEM in a Rattle Can.