Actually, there's a Czech company producing a 1:48 B-36 kit in fiberglass and resin, I'm guessing this is the model in question. I assume they use fiberglass for strength, due to it's size (the completed kit has a nearly 5 ft. wingspan!):
http://www.hphmodels.cz/hph/b-36-peacemaker/?lang=en
Sorry I can't help you with construction, but I know they use fiberglass in some RC boats and airplanes. Maybe look into RC construction techniques.