erniet.......On your diesel coach engine the fuel is pumped at high pressure to the engine. It doesn't necessarily use all of the fuel and returns a large amount to the fuel tank. When it's cold out, this helps to keep the fuel from gelling while the engine is running. I'm guessing your Onan generator works under the same principles. You may cause a fuel delivery issue if you put in a check valve.
Have you really had a problem with running the generator dry? I did it once since I've owned the coach while driving with the A/C on. Once I refueled, I pushed the prime button on the generator and it started right away.
Don & Mary
2014 Newmar Dutch Star - All Electric - 450 ISL
2016 GMC Canyon 4WD Crew Cab