When purchasing my 2014 Chevy Silverado (see my signature block below), I had already inquired from a 3rd party company about an under carriage spray on rust protection. Got all the info and then closed the deal on our truck. I made a comment to the dealer after I "owned" the keys I had an appointment set up to get the under carriage treated. He said I didn't need to do that. I asked "Why?" He said my truck come from the factory now, already treated. No need to do it with a new vehicle. When he told me that, I immediately crawled under the truck, right there in the parking lot of the dealer, and sure 'nuf, it's got some kind of coating under there.
Soooooooo....... If your vehicle is NEW, you might check with your dealer before spending money on something that has already been done. I guarantee you, if you go to a 3rd party and want the under carriage of your vehicle treated ... they WILL do it, and never tell you it was already done.
Check with your dealer if it's already done.