No snake oil there or here.
First one slight clarification ..... the HONDA EU1000i generator is not a 1000 watt generator ..... it's a 900 watt (continuous) generator - so the OP's MSH3012 would have to be set accordingly.
What the MSH3012 is doing is completely doable and believable. If the air conditioner's compressor-on time is enough less than it's compressor-off/fan-only-on time .... then the batteries will get slowly charged by the Honda over time since the fan takes far less power than the Honda is capable of delivering whenever the compressor is not running. If the air conditioner's compressor-on time is greater at all than it's compressor-off/fan-on-only time, then the batteries will get slowly drained over time even though the Honda is running full blast.
However, that slow draining mentioned above will occur WAY SLOWER than trying to completely run the air conditioner off only the battery-inverter combination. So ..... depending upon how hot it is outside, versus how big the interior volume of the RV is, versus how well the RV is insulated ..... the little Honda EU1000i/MSH3012/battery combination will either "run the air conditioner" until the Honda fuel runs out of fuel or "run the air conditioner" until the batteries eventually run down.
What the OP is doing would also work with my smaller Honda EX650 650 watt generator. Everything about what the OP is doing will scale accordingly depending upon all the variables.
What the MSH3012 makes possible is similar in principal to what Sportsmobile is talking about in this link - after the page comes up, click on the "Running Your Air Conditioner — When Parked or Driving" tab:
http://www.sportsmobile.com/heating-cooling/
