I’ve had the same problem since I bought mine 13 years ago. It’s garaged all the time and seldom, if ever, driven in the rain. Kansas City has high humidity in the summer and I’m guessing the odor is from moisture building up on the condenser and vent walls, which then tends to get mold/mildew growth. To help prevent the growth, I run the heater on high for a short time before turning the engine off to try to dry things out. When the smell gets bad, I put the windows up, turn the AC on high, and spray a can of Lysol in the intake in front of the windshield. I’ve had the same problem with a couple of other cars so I know this is not unique to Crossfires.