Just been outside to look at mine, it's rusty, but imho not rusty enough for it to be an issue over the lifetime you'd expect the car to operate over. Strangely enough my Panda which is a 4x4 and a 56 plate (500 is a late 09 plate) is less rusty underneath. The suspension is similar to the 500's although the beam has been cut in two to create two trailing arms with a mount inboard of the spring cups for the droplink to connect to the anti-roll bar that the 4x4 has at the back.