Although each site varies in length, their website says they can accommodate up to a 45' RV. When you click on a spot on the site map, it will show what size RV will fit in that spot HTH!

45 feet

Just about any size - the permitted length of each spot as specified on rec.gov is just for the pad. There is a generous amount of additional space at either end. Turns are not difficult to manage either but read the reviews by others with longer rigs.

According to the NPS website, the maximum RV length allowed is 45 feet. https://www.nps.gov/orpi/planyourvisit/twin-peaks.htm