An Oasis report will tell you the in service date. Also if you have any service done at a dealer the paperwork will show the original in service date as well.
Here is some information right out of the 2008 warranty guide:
Your vehicle’s body sheet metal panels are covered for an extended
Corrosion Coverage Period, which lasts for five years, regardless of miles
driven. The extended warranty coverage only applies if a body sheet
metal panel becomes perforated due to corrosion during normal use due
to a manufacturing defect in factory-supplied materials or factory workmanship. For damage caused by airborne material (environmental fallout) where there is no factory-related defect involved and therefore no
warranty − our policy is to provide free repair of paint damage due to
the airborne material for 12 months or 12,000 miles, whichever occurs
The New Vehicle Limited Warranty does not cover surface rust, deterioration and damage of paint, trim, upholstery, and other appearance items
that result from use and/or exposure to the elements. You, as the owner,
are responsible for these items.
Your cab and exhaust rust more than likely will not be covered.