I think a lot of the confusion is while you made a statement about not messing with the battery bank/solar array, you keep asking about a 3000w inverter.
To utilize a 3000w inverter, you need an upgrade to a decent size battery bank and a way to charge it (typically solar), so the presumption is when you kept asking about a 3000w inverter, you were still going down the battery bank/solar array path even though you stated otherwise.
I really suggest reading up on the subject. While there are some RV specific books, you might try a boating one as the cruising world has a longer and larger history off grid power generation. It's really not that hard but there are a few concepts of how voltage/watts/AC/DC/Amps work that would make this discussion much easier because you are mixing and matching without understanding.
As stated in a prior comment, if you don't understand and don't want to understand, hire an electrician to set it up for you. If you want to understand there are some good books out there or you might check with your local community college as they might have something.