Can a pvc door bow in the centre?

Yes it can, this could just be set up wrong, the keeps which the door locates into may need some adjustment, the door is being pulled in at the middle and not tight at the top and bottom, to adjust, all you need is a phillips screwdriver and a lot of patience.
the keeps have a screw at the top and bottom of each, (do not remove the screws, just loosen them as the keep will drop!) loosen the centre keep and tighten the top and bottom ones until you get an even seal all round the door.

carl
August 2010