Bill, if you are going to add that 20-amp leg, you will need to modify the circuit like Ziggy suggested. You *absolutely* need to add the contact relay to prevent an inadvertent short that could destroy your coach. As well, you will need to have a 4-wire (eg "50 amp" shore line - actually it's a 30-amp 230 volt line).
As for raising hell, you may want to ask a local attorney for his take on it - you may have a case for damages. If this is so, the Cummins/Onan dealer may opt for the less expensive route of fixing up your old genset and restoring what you had, particularly if they still have the old unit.
Hope you can get it to together.
1987 Excella 32-foot
1999 Dodge Ram 2500HD Diesel