I'd use fenders and hood but not doors, simply too many issues there. By the time the door is rigid enough to repeatedly latch and re-latch at post to open/shut correctly it will be as heavy as a steel door. Take Corvette doors for instance, same weight. The latching location points-in-space move around more with that type of material. Chase like Focus hood latch locators long term and you get the idea. The radiator support is metal support with FRP poured around it to mimic fiberglass type part, longterm they keep moving around to make for hood latching issues. Nothing guarantees positive locating of points in space like a metal part. You can adjust the metal part by simply distorting the metal, not an option on a fiberglass part.

Not having a metal impact bar inside door could easily fail inspection if a street car. Here in Texas they can turn down any single part which is not OEM, claiming it is not approved to be safe. Part of the inspector prerogative clause.