Powder coating anything that lives under the vehicle is a waste of time and money. Just my opinion. After all it is a daily driver not a "Trailer Queen". Have you given POR15 any thought? I think it may be the perfect solution. It bonds well, it is flexible, it's easy to repair if scratched, it encapsulates any rust that may be hard to get to when prepping, it's easy to apply, and best of all it's just about impervious to everything. I've used it in many applications and have had very good results. Just something else to think about.