With that length I would forget about camping inside the national parks and most US Forest Service campgrounds. Easy enough to find a private RV park where your trailer length will not be a problem and these will also have full hookups. Only difference is cost.
When we travel around the western USA in our 24' long RV we stay 95% of the time in public campgrounds and as a senior the cost averages out to around $7 a day. At a private RV park the cost is going to be over $35 a day (though you do get cable for your TV and free Wifi). In the private campgrounds you also will not have to deal with generator noise which is a blessing.