I wish to replace my single garage door with upvc French doors, my house is of timber kit construction with brick outer leaf. I have a set of French doors I got for free and want to use these. The problem is the doors are 400mm short on width, but the height is O.K. I was going to fill the gap with a frame made of 75 x 50 mm timber, 200mm either side, and bring internal walls to meet door frame,and covering the exterior with upvc sheet would this be the best soloution? Gap is too small for double glazed sidelights.