Piper built a single prototype of their Papoose light trainer. It looked similar to a Cherokee, but was mostly made of fibreglass composites. One journalist blamed its demise on a dispute with unions over reduced man-hours to manufacture compared with sheet aluminum Cherokees. OTOH I suspect that fibreglass technology was not nearly advance enough for FAA certification. Look at all the certification hassles Windecker Eagle and Beechcraft Starship suffered.