The undercarriage of my 69 Chevelle has minimal surface rust. I was able to remove all of this rust with a wire brush. Should I just use some type of chassis spray paint or go all out and go through the POR 15 process? This is a southern car and isn't driven while the roads are wet. I don't want to spend extra time and money if it isn't absolutely necessary.

Thank you

Down south I would say it is overkill. POR is nice but very messy. You will still need to top coat the POR which makes an extra step. WHat I would do though is use POR metal ready. It is an acidic zinc type product. It sprays on and hose off. gets rid of any corrosion. It gives some rust prevention. Then just spray your chassis paint over that. I use POR a lot and am not really that impressed overall. Brake fluid eats it right off. If you paint it on rust it really sticks. On clean metal that is not blasted it can peel off in a plastic sheet just like powder coat.

Por likes deep etching like 36 grit sand paper. sometimes 80 grit will suffice. It really likes rust to bond too kind of sounds silly but that is the way it works.