What is the best way to repair the holes caused by rust in car body .
This is for my friend's car and the car has couple of rust holes on rear wheel arch.
There are two holes sized 2"x1"

I have some idea about this "Bondo" or similar material .I have seen it at Walmart
I think one car buy the fiber glass cloth ,epoxy and a third material in a kit.
I have never applied this thing.
How is cloth fixed to metal body of car or is it simply held by the epoxy in Bondo.
What are the tricks of using this thing.

The other option I was thinking was of another material called mattle* something .I forgot the name .
It is epoxy putty contains metal particles etc can be drilled etc
It comes in the form of small 2" long stick .
The stick is made of two concetric cylnders of different materials.One has to kneed it together
I like this as I was able to close 2-3 rust holes in cars floor pans.
The only diffculty I see is that it solidies within 3-4 minutes and I do not know how well it holds the paint.
It is costly also

I think one has to do some sanding after fixing this . What grade and type of sandpaper one should use.
I am also thinking of applying the paint directly without any primer etc.Any concerns with that
Regards
Gopesh