Suggestion.. Do what I did (in this case this is not "DO as I say" it is "Do as I did")
I obtained a proper Generator Transfer Panel and INLET from either Lowes or Home Depot.. This is a panel with several switches on it, the one I had also had watt meters to show how much power we were pulling off the generator.
Now the ONAN is a 120 volt device, Most of your NECESSARY systems can run on a single 30 amp feed in the house.. If your motor home is 50 amp however you can likely pull two 30 amp feeds. THough if you do that the neutral wire can hit 60 amps so bear that in mind when you modify and install.
ON the motor home I put a set of outlets in a weather protected location.. Two 30 amp female (TT-30's) and one 30 amp Twist Lock I used the same Twist lock as on a portable generator I had (For obvious reasons, same cords fit). Alas the generator grew legs and walked off on me, I think I know who's legs but think, and prove long distance apart.
In the house: The generator panel went next to the main service box.. The one I had hooks up like this.
You remove the branch circuit wire from teh breaker, Connect it to one of the wires from the transfer box, (Wire nut and tape) connect the mated wire from teh transfer box to the breaker (The wires are all numbered and coded to make sure you put the proper wire on the breaker) You also hook up a heavy neutral and ground wire.
I extended the "INLET" on the box to the back wall but you could put in a standard 30 amp round "Electrical Hatch" (Any RV store) and run teh cord to the transfer box.
I made up a special long heavy duty (8GA I think) cord
When the lights went out (Not if, but when, alas, modern power companies do not believe in reliable service) I got the cord out of the basement, One end to the house, other to the motor home, Fired up the ONAN, and back in the basement started flipping switches,, This was Dec-31
CLICK light
CLICK furnace
CLICK, Click Click, fridge, freezer, Computer, Television/radio and so on.
I left one light on the MAINS, went up stairs and turned it on (It is a hall light on a hall that is perhaps six feet long, We almost never turn it on) When the light came back on it was down to the basement and click everythign back to MAINS, back to the moto rhome and say "Good night" to Mr. Onan.
One cord, No rat's nest and no breach in home security (You might note I'm FROM Detroit, Home security is important there)
Later,, (This was the last half of January) In Quartsite, one of those TT-30 outlets came in handy when my neighbor's generator refused to generate.