New car corrosion prevention/undercoating

I'm planning on buying and 05 Xterra when they come out. I'd like to be proactive about preventing frame rot, since I'm hoping to keep the car for 10+ years. I live in north east Mass, and road salt (and maybe the salty air since I live near the ocean) became an issue with my

I haven't bought a new car since 1994, and seem to recall that the dealers use to try to sell you undercoating which was generally regarded as a joke to sucker you out of some $$$. (I don't really recall, maybe I refused it on my pathy and that's why it's frame rotted!)

What's the latest on this? Do dealers still try to get you to buy undercoating? If so, should I get it, and does it do any good? While we're on the subject, what about rust prevention treatments for the body?

I'll thinking about using one of the POR products, or maybe spray on truck bed liner on the frame right after I buy it, but would pay the dealer if they offered something that does some good.

Either way, I plan on paying attention to this through the life of the car so it doesn't get to the point where my pathy did. According to the marketing literature, the 05 Xterra's frame is a "corrosion resistant" steel so it may be more resilient anyway.

Thanks - John