How to keep clean?

[Iamamini]

Hi! I washed the car today and felt better doing so, the salt and more makes it a pain to keep the car clean this time of year. My main problem is this: I got a white roof and at the back of it where the roof meets the boot (not visible from the outside) there is no clear coat at all. This makes it harder to keep clean , and that white part under the boot lid on top (rest of car is Indy Blue) is not all white anymore, I can see small black particles there that is "stuck" in the white paint, and some discoloration. It is not that bad, but I am concerned it will get worse and one day I may get rust spots here. Today I tried to clean it as good as I could and then put some wax on it to keep the dirt away. Do u have the same problem and/or have u found a good solution for it? Maybe putting wax on that no clear coat color is not a good idea? If so, what should I do?
I am not nut about this thing, it is not the end of the world, but I want to prevent rust if that is possible .