I install a lot of doors for a local lumberyard. They can't get an off
sized door of fiberglass as the panels are cast onto molds to determine
the length. It is a solid sheet of resin and fiberglass scrim.
When you cut fiberglass, it is shatters and splinters. I tried cutting
it, grinding/sanding, and all other types of removing length. No dice.
The cut edge was OK at best, but when stained or painted it really
The added problem also was that I corrupted the structural integrity of
the door as I cut off part of the frame panel. Oddly, to make an off
sized door of fiberglass, our local door plant charges just about the
In your case, you would have the added ugliness of a thinner side piece
(stile) on one side than the other unless you are just putting in a
flat door with no panels.