I looked into this when I got my Progressive hard wire unit. If I remember correctly when using the gen the E-2 error comes on and it means an open ground or open neutral. Some fix this by plugging in a replacement plug, one used to fix a bad plug that you have to wire to the broken cord, into one of the 110v plugs on your gen. You have to wire up the plug by running a wire to the neutral and to the ground. This supposedly closes the loop. I wired the plug exactly as the instructions said that I found on the internet. I made the plug but still got the error
In the end I just turn it off. The panel has an on/off switch. From what I have read Gen power is clean and steady and it doesn't require the unit to be on. Since the gen is only powering your rv you don't have to worry about the power being used by hundreds of other campers which lowers the voltage.
So now If I'm running the gen the unit is off. Never had a problem.
Hope this helps.
Jerry