On steel-bodied vehicles, I DIY it with stuff from AutoInt and Eastwood.
My Mazda MPV, kept in immaculate, show-quality condition, is constantly rusting from the inside out, and no, Mazda isn't any help. When I was shopping for Suburbans/etc., *every one* of 'em had rust starting in some places where normal people don't look, even the ones I looked at down south (when I finally found my rust-free Yukon XLD I bought it in a heartbeat, and rustproofed it myself). I found rust lurking in some out-of-the-way places on my seemingly nice M3 too. And you can just *guess* how the Beater-Blazer was in that regard
Some of my Benzes and (steel-bodied) Audis never had a spec of rust, but they weren't Chevies either. And they were kept immaculate year-round; how much time do you really plan to spend on the undercarriage every week?
I'd at least buy a few aerosol cans of AutoInt/ValuGard Rust Inhibitor and/or some Eastwood Heavy Duty Anti-Rust. See if there are any known trouble areas that others have discovered. Open up the door panels/etc. and shoot the seams from the inside. Do the hood (MPV's current inside-out rust issue) and the trunklid too. The long applicator nozzles on the cans make such work easy.
If you buy the black version of the Eastwood stuff, you can do a really nice job on the undercarriage; it looks almost like black paint and it's easy to keep looking nice.
I also spray some undercarraige/underhood spots with Amsoil Heavy Duty Metal Protection (I think that's the name). Great for electrical contacts/grounds and fasteners that you don't want rusting solid.
A little work when the car is new and still rust-free can take such concerns pretty much off the table. Well, as long as you still keep things nice and clean (dirt harbors moisture and moisture leads to rust).
I'd be *very* leery of having it done by a pro. Some shops/guys are VERY good, but IMO those are few and far between and a hack could mess up your new car.
