Yes, all you need to do is connect a 50 amp female to 30 amp dog bone to the shore power cord and then put a 30 amp female to 15/20 amp male dogbone on the end of the 50/30 amp dogbone into the 30 amp female end of the 30 amp to 30/20 amp dogbone and plug the 20 amp plug into the inverter. You could also make your own adapter using a 50 amp female receptacle wired with both hot sides of the 50 amp plug connected to the hot side of the 20 amp plug. I would just build it in a 4" square electrical handi box with cord restraints on each cable. Just buy a 50 to 30 amp adapter and cut off the 30 amp plug and use that as the input cable. You can easily make your own 20 amp side with a short length of 10 gauge SO cord and receptacle end.
