I'm going to use Carpotech RX5/RX7/RX10.
Got some left from my Alfa-Romeo days. These product were highly praised within the AR-community.
Alfa's are known for their weakness to rust, so if this stuff can keep Alfa's from rusting it sure would be enough on the Crossfire

Basically the RX5 encloses the rust to keep it from getting worse. RX7 is used as a finisher for unexposed panels (inside doors/sills) and remains flexible and protects against moisture. RX10 is used for parts exposed to the outside weather and is a hard&thick protective coating.
I will be using RX5/1010 for the winner wheel arches (collect a lot of dirt) and on the notorious door spots (trap moisture) only..
I won't paint any more surfaces since all other places of the car are fairly easy to clean. Better spot rust when it starts and is easy to repair than to cover it up and discover years later when it's too late.. (been there, done that )

I cleaned the undercarriage last week and it was still almost mint condition, despite the Dutch weather and the car being used on a daily basis. Looks like the crossfire has some decent rust protection in the wheel wells and undercarriage. Only real weak spots I found were the inner front+rear wheel arches (no coating).

I e-mailed my RX-supplier and he said it can be used over paint on non-rusting cars (so far i have no rust except the doors). If you have any exposed pieces of metal due to chipping the RX5/10 combination will seal and treat these. On places without damage the RX5/10 combo will become an extra layer of protection.