I would not assume the panels from LMC truck are made in the USA, unless told otherwise.
"And if you apply PPG DPLF you can also try the lacquer soaked rag on it, but be prepared to substitute something better and cheaper like SPI when it wipes right off ."
PPG DPLF is a base coat. It is intended to be topcoated with a paint. I do not normally park my cars, when they are in primer only, were it rains lacquer thinner. I would also think that if the undercoat gets softened by the solvents in a topcoat, that would only help the bond between the primer, and the paint.