From Utah.
Congratulations on your return to camping. Our outfit is very similar to yours and one thing I've found is not all campgrounds are set up for our size campers. One big difference is the height clearance. Also an issue is the actual site size. Some parks and campgrounds base their space size on the total length of your outfit. Others just the trailer. Most RV parks have pretty informative web pages with specific site sizes and other specs.
We don't use a specific app but do use
https://www.recreation.gov/ when planning to use any Forest Service or National Park campgrounds. Also,
https://www.reserveamerica.com/memberSignInSignUp.do for State Parks. It hasn't mattered which state. So far, they seem to all use the Reserve America service. If you are not familiar yet with these two sites I'd recommend giving them a look. RVing has become so popular, getting a campsite requires some long range planning. Up to 6 months in some cases.
Another idea, once I've decided on a campground, I use Google Earth to get a "birds eye" view of the area and specific sites. Hope this helps. I'm sure others will chime in with specific apps for route planning etc.
Camp Safe and Camp Often.