One point... if you restrict yourselves to sites with electricity, you will be missing out on a lot of great campgrounds. National Forests have some of the most beautiful campgrounds around and very few of them have electricity.
You can stay somewhere a long time with just decent battery capacity, but not use electric cooking appliances (would require a generator & inverter.) So you might want to develop an alternate cooking plan based on using propane and campfires. Also if you have LED lighting in your RV you will greatly reduce your electric usage.