Yup- you can not use two regulators in series. The gas line coming from the RV is past the regulator on my Thor Vegas, so you need to find a grill that you can bypass or remove the regulator.
I got this grill:
https://www.campchef.com/ranger-ii-t...ner-stove.html
Works great with a gas hose that has a 1/4" male quick connect to a female (i think 1/2") threaded connector.
I also got a big buddy space heater as it has a direct connect propane attachment. You need a 1/4" male quick connect from the RV to a female 1/2" quick connect hose to the space heater. I had to order an adapter for the 1/2" quick connect but it should work out well.
Anyways, the lesson is that if you want to use a propane appliance you can only have 1 regulator.