Mine was apparently painted from the factory (although that was decades and and unknown number of owners ago, so who can tell?) and is currently sort of beige, where there is any surviving paint
at all. Most of the frame surface under the trailer (but not the tongue or bumper areas) has almost complete coverage by surface corrosion.
The original manual definitely says to touch up areas of damaged paint (so it must have had paint) to prevent corrosion; that was apparently not done by previous owners.