Thanks for all the great recommendations. After all of the input I figured it's only fair to stop back in and update you guys on what direction I went with it. My body guy and our local auto paint store guys both ended up telling me that I'm going to want to seal the underside with an epoxy primer and then paint it with any old flat black paint that I want to. I'm told the key is to use an actual 2 part epoxy primer with an activator. Our paint supply store had some Spray Max 2k epoxy primer that came in an aerosol. This stuff had a button on the bottom of the can to break a canister on the inside of the can and allow the activator to mix with the primer. It only came in beige, so I had to run some flat black over it to make it look right. If you're looking to do the same you can probably get away with 3 cans of the primer if you spray it on just right but you should probably use 4, 5 if you want to get thicker with it. It was about $25 a can from the paint store but it's probably cheaper online. I'll probably still put a little rubberized undercoating above the tires. If I remember I'll stop back at this post 10 or 20 years from now to let everyone know how it holds up.
