I really like the JD buff primer on bare metal seems to adhere and last really well.

Very neat idea on making your own down draft paint booth what did you use to exhaust the fumes ?  Could maybe be an issue if your not using some sort of explosion proof motor on the fan. Also be sure to use a good respirator when spraying that hardener it's very hard on the lungs.

Looks like a very good quality job you are doing hope you will post more pictures when you are all finished.