Try removing the coolant fill cap and run the genset and see if trapped air is expelled. Have you recently drained and refilled the coolant? If so, trapped air can prevent a full fill and you may be getting a low coolant shut down.
Now, if you have not recently drained coolant, you may have a failing temp sensor. Onan QD gensets have a sensor installed in a fitting at the top rear of the engine that, when it fails, will tell the genset it is overheating when it is not and will shut down. If that is the issue, the top of the genset will need to be removed to get to the sensor for replacement.
Just a suggestion but I would not take your QD to Camping World for service unless you have prior experience with them and trust them. From my experience, they do not generally have the skills to do much other than very minor work. Your best bet is to find a Cummins Coach Care or Cummins/Onan shop and have them take a look at the genset.
2007 Country Coach Allure Siskiyou Summit, sold/traded Nov. 2018.
2019 Grand Designs 384GK-R 5th wheel. Glen Allen, VA