For a reasonably priced exhaust fitting, find a Planar dealer (the Russian heaters - "made in Russia by people who know cold"). They have straight, 45 deg, and elbow. The heaters themselves aren't bad. Note, their exhaust tubing is thinner wall than that sold by Espar dealers, I don't use it. Their insulation wrap is good, about $30 for a 25ft roll. I do a fair number of these installs & servicing, Webasto, Espar, Planar, Hurricane & Kabola. I would never have bare exhaust except in a stack where dry engine exhaust is accommodated. I use two layers of insulation and can put my hand around the insulated pipe without being burned. I will form any bends, wrap the whole pipe and secure with wire before putting in place, then additional wrap over the clamps, leaving no hot surface exposed. Residues on the tubing will make some smoke and odor initially. Exhaust temp of 400F or more is normal.
Without the double wall, the exhaust fitting temperatures will damage fiberglass, probably won't ignite it but I would not take that chance. Fiberglass when ignited can smolder and creep along ever so slowly undetected until it encounters some better fuel like wood, or a chimney effect or other steady air movement and you can have fire break out hours after the original ignition. I've seen where it happened and traced it back to the cause, a shore power inlet in this case. The fire broke out 7 hours after the cord had been disconnected. It caused $35K damage. I swear the FD dumped 200 lbs of dry chemical agent on the boat.
