Rusty wheel arch

[ron]

I have a 2 door coupe and my driver side rear wheel arch has stared to rust Its only on the flat edge just above were it tucks under the arch, and about 9 inches around. I have filled and repaired this before but it always comes back after a while, this time I am going to weld a capping on and it should last a lot longer. Having looked at a capping for a coupe and a 4 door the price difference is quite dramatic in favour of the 4 door. My question is, does anyone know if the shape of the actual arch itself excluding any extra metal and shaped parts for the door are the same for both the 4 door and coupe, considering I only need the middle part of the actual arch. This i would trim off of the panel in either case. would like to know if anyone has used a 4 door arch on a coupe before.