If the damage came from a farmers sprayer, being towed, then there would be "tale-tell" patterns of the etching.
If not, then it is most likely acid rain or industrial fallout which when subjected to moisture, such as dew or light rain, will activate the acids on the paint, resulting in etching.
The paint job from the assembly plant is not "faulty" for if that were the case, the damage would have shown up within a year or two.
Read you owner's manual and I beleive it will state that the paint is warrantied for 12 months against "factory defects", IE the damage that occurs due to enviormental conditions are not covered once the vehicle is sold.
As far as getting insurance to pay for this concern, doubt it.
You would need to locate the farmer, find out what was in the sprayer, etc and then his insurance would cover the damage.
Never saw or read an auto insurance policy that covered the owner for damage such as you are experiencing.
Not sure where you are located, however if the vehicle is operated and parked in industrial areas, refinery's, etc, that may be where the damaging compounds came from.
Grumpy