Congrats for getting out of So Cal!!! I left the Republic of Kalifornia 11 years ago and have nver been happier!! Por15 or one I like even better is KBS coatings are the only products I would truly trust to stop and seal the rust. I am restoring a 77 CJ5 and it will be as close to rust proof when we get done as possible. I am using the KBS, a little goes a long way. A 1/2 gal would treat everything underneath, however you have to do the proper prep work. Undercoatings usually only work on a new vehicle, otherwise you trap this junk and as already said it will just rust faster. You can cut corners and cost, or do it right the first time and know you are protected. PM me with any ?