2 ways i would suggest:
line up early in the morning (i think the office is open at 9am and a line was forming at 8am) and maybe get a site or
look around upper pines or lower pines campground for a site with one small tent. ask the people if they are willing to share and pay half the site cost (price was $20 bucks or so a site last year). Camp sites are massive and it's a joke when they say it's full when there is space everywhere.
There are showers close by. To get around eg to camp 4 just catch free bus right next to campground.