I've been doing this for years ( portable 50 amp progressive and buildt in one now). No problems. I have a problem that came up this year with it seems the onboard hard wired system. The portable Progressive is fine and reads what is going through the the transfer switch ( had it tested current coming into the transfer switch).
However for some reason the onboard is showing higher shore voltage than what is actually coming in. It shuts down power occasionally even though the portable one is still allowing current ( not indicating high voltage). If I disconnected the portable when this happened it still shuts power down connected straight to the post, even though there isn't a high power ( checked at post too). After a few attempts reconnecting power it works.
Funny thing is,if it shuts power down and I run the generator it's fine and reads voltage correctly. I'm have it looked at in January.
It must be something with my onboard surge protector as other MH's in the same row didn't have a power issue.
So in my situation it actually shown me (having two) I have a electrical problem with the onboard surge protector.