Saw a few GM frames at our recent Fleet Show - the Medium Duty Silverado 45-6500 is a glossy black, which saves a step for the upfitters. Same for the Isuzu based Low Cab Forward.

The HD Van frames (Express/Savana) are dipped the same way they did Impalas 70 years ago, looked like an asphalt type coating, with lots of runs and drips.