LOSP is my favorite campground! There are only basic and electric sites here...but you can fill your water tank at the campground entrance, there is a dump station to the right just past the check-in booth. Only the sites in the 150's by the lake for the most part are big enough for long campers...Some of the other pads are long, but you have a steep hill at the bottom of the site or there are too many trees around them to get into with a long rig. Your best best is up the hill in campground 3, which has some electric first-come and reservable sites, and a reasonable walk to the lakefront down a path behind the amphitheater.
Weekends book up many months in advance for any of the trout parks (Bennett, Montauk, Roaring River).
Missouri State Parks Website has a list of campgrounds that have full hookups, not many. Table Rock Lake State Park has full hookups in the section that is right by the Marina.
The Corps of Engineers have many campgrounds in Missouri and they often have full hookups. We used to camp a lot at Ray Behrens which is on Mark Twain Lake near Hannibal. You can get to the lake from the campground there, but all the paths are down steep hills. Still, it is a pretty place, although not as nice as Lake Ozark State Park. The COE book their reservations through
Reserveamerica Thumperpull, if your rig is rather short, you may be OK with some of the lakefront sites; be sure to look at the photos of the sites on the State Park website and make note of the grades.