For rust treatment you can look for Noverox. I'm not sure if it's avalaible over there. You have to paint it over the rusted areas and as soon as it starts to work it changes the chemical composition of the rust. After its done, it won't rust further. Then you can smoothen it with some sand-paper and paint it over. Works great, i've used it on all my cars.

Never heard of Noverox, but i will surely see if i can get it here. Otherwise you could send me a package
I asked a friend to take a look under the car, reading the inspection papers, there never been any complaints about rust during the years. Lets hope it will last.