Toddlite, there are multiple parts to the answer to your question.
1. Bad news: There is no way to do what you are suggesting in a manner that complies with the National Electrical Code.
For an installation to comply with the NEC, the inverter must be designed, built, and rated to connect to a vehicle's electrical panel. Yours is not.
2. Good news: An inverter that is used in a vehicle or marine application must carry a UL458 rating. Your Xantrex ProWatt SW IS UL458 rated, so that's a good thing.
What does UL458 have to do with anything? In a residential electrical system, neutral is bonded to ground at the electrical panel. A vehicular electrical system is a little bit different, because sometimes the vehicle is plugged into a ground-based electrical system, and sometimes it is not--and you cannot bond neutral to ground in more than one location.
The short story is that a UL458 inverter will bond neutral to ground when it is not receiving AC power. Your inverter is not designed to receive AC power, so it is built to always bond neutral to ground. On the other hand, inverters that are designed to receive AC power (see discussion of pass-through power, below), have an internal relay. When external AC is present, the relay opens, and the inverter does not bond neutral and ground. When external AC is not present, the relay closes, and the inverter bonds neutral and ground--just as yours always does.
For more details, see post #6 in this thread:http://www.sportsmobileforum.com/for...ter-19021.html
To summarize: you have an inverter that has the correct UL rating for use in a vehicle, but your inverter is not designed, built, or rated to connect to an electrical panel in that vehicle.
3. Connecting to a vehicle electrical panel
This is a conceptual sketch of how an inverter should be wired into a van's AC system.
In order to do this correctly and safely, the inverter must have both AC input and AC output terminals (and the neutral-ground bonding relay discussed above). Your inverter has none of this.
A couple more items to note:
You want the items powered by the sub-panel to have power available to them when you are on shore power. This means that the inverter must have "pass-through" capability. Pass-through means that when the vehicle is plugged into shore power, AC power enters the inverter through its AC input terminals, passes through the inverter unchanged, and then exits the inverter through the AC output terminals, and enters the sub-panel to power those loads.
If you do not have this arrangement, then the only way to power your sub-panel when on shore power is to have the shore power energize a battery charger, which charges the batteries, which power the inverter, which energizes the AC panel.
That's not a practical or safe setup, and it definitely would not comply with the National Electrical Code. Among other things, it means that you will have neutral to ground bonding at both your inverter and at the shore power panel.
Bottom line: while there are inverters that are designed to be part of a van's AC electrical system, your inverter is not. Attempting to kludge the system to make it do so means engaging in electrical no-nos, which generally means creating fire and/or shock risks. Unfortunately, you should either live with the inconvenience of the outlet locations, or buy an inverter that is designed for your desired application, and wire it in a safe manner.