I don't know any of the details.  HPH used fiberglass because of the cost of injection molding and it allows for a strong, thin shell.   Resin would be even thicker and not structurally sound anywhere close to a scale shape. Both Plastic and Resin would lead to serious inaccuracies with the finished model shape and/or interior details.     All I Know is I have seen 3D printed parts for most of the interior and one engine and that it is not GT Resin.