Headless,
the CX chassis is closer to the Aero Chassis in that it is made up of pieces of aluminium, sheet, extrusions and some casting/forging pieces, all glued together. The under surfaces, at least on Tarka, are undersealed. I'd expect the CX chassis to be undersealed.
As with virtually all aluminium chassis cars they are designed to be used in all weathers and are less sensitive to corrosion than steel. Some aluminium alloys develop a surface corrosion which then protects the body of the metal. I don't know if MMC use this type of alloy anywhere.
If I had a CX chassis car I'd treat it as a modern, all weather, car.
Enjoy the future!
