Acropora

Should we get cars under body's rust proofed?
We salt heavily here in the Midwest and our 2007 GL450 has some evidence of rust on the mufflers at least.
Just wanted to do it before any road salt gets at the undercarriage if recommended.

Chasvs

If after 7 years all you have is a little rust on the mufflers I think you're OK going with the Manufacturer under coating as delivered. These cars get multi coated anti rust protection at the factory which is why the rust warranties are so good these days.

ciparis

Aftermarket coatings have a tendency to capture moisture after a few years, especially if their application was less than perfect -- potentially leading to a much worse problem of deep, hidden corrosion. Personally I would never let someone attempt to apply it. Just be sensible about your car washes, and give her a good rinse a few times a season (and especially after heavy snows have been cleared).