Detailing a Benz

So far, I've gleaned some good info from Usenet, for caring for my upholstery, namely Leatherique.
I've also learned that X-treem Majic is good to use on Aluminum.
Anyone got any other detailing tips? I'll compile the ones that I use, here;
What do you call the gray 'underbelly' portion of my vehicle? What is it made of and what's the best product to clean and protect it? The Prestine Clean from Leatherique, perhaps?

best regards,
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