The three way switch is eliminated.
The WFCO is a good basic three stage charger/converter/power center. You might want to consider the 8725P to save some money. It should be sufficient for all your needs.
Residential receptacles only meet code if they are in a box. RV and mobile home receptacles do not need a box. Any receptacles should be GFCI protected.
The red wire from converter goes to the battery, the charge line from tow vehicle goes to the battery. All negative/grounds go to the frame.
Your WFCO will have positions for breakers. You can get the breakers at your local home improvement store. Use a 30a breaker as the main by energizing the buss bar through that breaker. Add 20a and 15a breakers as needed for other receptacles.
