i can't answer questions specific to Road Treks because we have had a Sporstmobile Sprinter model.
Campsite occupied sign - Worthwhile - we use to have one but it was either stolen or misplaced. Most campgrounds assign sites and many have a little tag that you leave on a post to show occupancy.
Showers and bathrooms - We use campground facilities whenever possible. We have never used the shower in 10 years and 110,000 miles.
Storage - What we have is fine for us. Models vary in forms and amount of storage. People vary in needs. Human nature being what it is, you will probably fill however much you have.
Drivers - my wife does 40-50% of the driving and is comfortable with that.
General advice, all free - Get the Good Sam travel/campground guide. it is invaluable for finding places to stop.
Get a Garmin or other GPS even if you have a built-in GPS system. You can find nearby grocery stores, medical facilities, restaurants, etc. etc. when you are in strange places - invaluable.