This is a schematic that goes along with the 120VAC selector switch shown above... They wired in several different 120VAC appliances in addition to what you was wanting to do. This just shows what you need to do to allow the 120VAC receptacles to be used from the two different 120VAC sources (Distribution Panel or the Inverter). You will need to adapt this to your wiring of a couple of 120VAC receptacles. This drawing was for the whole Distribution Panel being selected between the Shore Power and Large sized Inverter. This is much more involved than what you are wanting to do... Just showing this to give you some ideas on what you will need to develop for your project. You will only need to switch a couple of 120VAC circuits - not six as shown here...
Roy