Peter, although I have used the POR15 on chassis and like it I will say that the 37 I have got the Black Gloss Rustoleum in 1997/1998 and it still looks good today. I even drove it in the rain today!! So, I think you will be OK.
As a side note a friend of mine used the rustoleum Primer and Black paint on his 37 and ended up spending more money for the rattle cans than it would have cost for the POR15. (or Eastwood's)
