I've used Allstays Camp and RV
for a number of years on an iPhone and iPad. It is also available in Android, but it's the Apple version I'm familiar with.
This is an excellent app and well worth the price. It is kept up to date and is still backwards compatible to older OS's so you don't need the latest hardware to run it. I've found recent versions of Trailer Life/Goodsam campground directory to be far less useful or essential than the older ones were. For me, Allstays has replaced TL and is much more pleasant to use.
For iDevices, Allstays piggybacks its info on top of Apple Maps so it needs a much smaller data base. You do need wifi or a data connection to get the map info, but carefully zooming the screen in the campground before we leave, preserves a screenful of data while we're driving and covers several hours of road time. I've found Allstays to be very accurate in location and they even have the new name of a campground we often use in our travels, and it just changed hands last year.