Newbie question alert!
Am I right in thinking the Up! does not come with rear inner wheel arch liners? Just seems very noisy over gravel and in the rain, also surely can't be good for the car long term with all that muck getting up into the arch....
I would, clean the under surface of the wheel arch and then spray anti-rust paint under the wheel arch and then as a next step open the boot, remove the liner covering the interior part of the wheel arch (from inside the car) and apply foam insulation sheet to it. Easily done and very effective and cures both rust problem and noise insulation. I have done that in my Aygo.
Stratcast, since you are from Norway, you can go to the nearest Biltema and buy two spray cans of anti-rust spray and the self sticking foam sheets with shiny lining, cheap and effective!
Same here, rust warranty only counts if the rust develops from inside a panel not outside! Sure, components etc rust quickly but the bodies here last well these days. Unless its an original Ford Ka, they rust everywhere like a proper old car!