Post Oak is kind of a partying park on weekends, and somewhat less developed than Washington Cove on the other side of the same reservoir. Post Oak is mostly primitive sites, and attracts more tent campers, while Washington Cove is more of a RV campground, although it can get pretty wild on holiday weekends (but not in April). While I've not stayed at Post Oak, I have friends who go there to party. In late April Post Oak may or may not be open, depending on lake levels and whether or not they've managed to attract volunteer hosts to manage the campground; it sometimes opens later in the season.
I don't know your travel direction, but last time I checked, Oklahoma Highway 10 was closed at the Copan Lake dam, as the Corps has been renovating or rebuilding this dam for almost two years. The detours to get to ad from Post Oak could be 30 to 60 miles off your logically direct routes, depending on how much you are willing to use county roads versus state highways and U.S. highways.