Thanks, Joe. I appreciate that.
Hmmmm, you don't have an airbrush? Well, you could probably do the same by using diluted acrylics, and adding the inner panel lightened patches using thin acrylic washes? Remember that whatever you paint, you have to be able to look BEYOND the immediate results of painting and envision it with washes and filters added. These can greatly soften differences in paint and tones. You wouldn't even see the lines of color delineation if you experiment a bit.
I used a popular pigments line for rust on those, but I'm not married to any one color, paint, or technique,. You can get all the rust tones you need from a few oil colors, including orange, raw umber, yellow, and raw sienna. With those colors, you can do just about any tone of rust or degradation you need.