After I used my RV just a few times, the flapper broke. Just as you mentioned it was the thin plastic hinge pins that broke. Coincidentally I was near the manufacturer (Northstar) and stopped at the factory. The were accommodating and offered me a choice of the only two varieties they had available. The first choice was identical to what broke. Or I could opt for a similar unit that did not have a hinge. The flapper was held in place by a piece of tape that looked like duct tape. I opted for the original which soon broke.
I repaired the replacement by using a piece of coat hanger as a substitute for the plastic hinge piece.
Anyway the overall design is just appalling. Even worse, the flapper needs to be secured for travel or it will continue to flap and soon break. I have to stand on a stool to secure or release the travel tabs. Since that is a major nuisance and the exhaust fan on my range hood is extremely noisy, I gave up using it. Instead I try to use the fantastic fan on the ceiling to clear smoke and odors from cooking.
Perhaps there are better choices but I have not looked recently.