Welcome to the forum.
A link important to Newmar owners.
If you go into the
QT's # 3 link and down into the second section you will find a section devoted to inverter/converter problems.
All the links below in my signature have answers for your Newmar.
You said you reset the circuit breaker for inverter is there also two push buttons to reset also, not sure you have them.
Now I see you said 600w inverter my inverter was plugged into a GFI outlet that at times had to be reset on the GFI outlet its plugged in to.
If you can't reset that, could be the outlet or the circuit breaker back in your load center.