It seems that they just use unprotected metal sheet, which will form a light coat of corrosion due to moisture in the air. Not really something to worry about, but they could have used some kind of protection at least.
JEEP Grand Cherokee 4.7 Lmtd 2004
HID 8000K in low and fog / Quad Squad member
KYB Gas-a-Just shocks / Pirelli Scorpion ATR 245/65/17 - Transgo reprogramming shiftkit.