question on using an inverter in my motorhome

Hi. I hope you're well. 

I have a small sprinter based motorhome with manual transfer for use of a generator. To use the generator, I just plug the line coming from the generator into the appropriate box in the shore power compartment that feeds the main load center. I want to install a 2,000 watt inverter (a Samlex SSW-2000 12A). I'd plug a camco 30amp cord into the inverter's 20 amp receptical then plug the other end of that cord into the same receptical in the shore power compartment that I use for the generator. 

The inverter's instructions say essentially to only plug devices into the front of the inverter (has 2 (20) amp receps) and not to connect the inverter to household or RV distribution wiring. The instructions say don't connect the inverter to any AC load in which the neutral is connected to ground or negative of a DC battery. To my knowledge on my motorhome, the DC is grounded to the chassis. I have no idea about the AC. The negative off the battery bank is bolted into the frame. 

I know exactly which circuits to use if I plug in the inverter. I don't plug in for shore power, so there is no risk of drawing too much current from the inverter, because I've shut down the breakers that can't be served by the inverter. 

Are the instructions saying I can't do what I intend to do or am I ok?

Thoughts are appreciated. 


John