All I can tell you is...I went on Labor Day and it was pretty busy...and HOT too. After Labor Day the crowds will calm down some but during August, it's still busy. I think if you can swing staying onsite, it will help you greatly.
I'm going this Friday thru Sunday (12-14) and staying onsite just for the convenience and FOTL pass. The wife and I are doing a little getaway without our son. I think the crowds will be very light on Friday and alittle busier on Sat and Sun.