I spent three months in Yosemite (not in the valley, but in the NW backcountry which BTW has amazing climbing opportunities, but requires some major backcountry traveling, no VW bus's allowed ) here are some tricks:
TIGHT BUDGET trip to Yosemite.....
my favorite trick to avoid overcrowded campgrounds, their associated fees, bears breaking into your car to steal your chub, and even avoiding paying an entry fee is to do the following:
Most parks like yosemite are bordered by Forest Service land. You are permited by law to drive on any Forest Service road, pull your rig over to the side and crash. No wake up calls from the law, no $15 charge, and you get some solitude. There are an abundance of roads off HWY 120 just outside of the Hodgdon Meadow entrance to yose. Some even are next to streams which provide wonderful bating ops. One road in particular is the road to Hetch Hectchy which is RIGHt outside the park entrance. What I've done in yose and many other parks is crash outside the park on these FS lands, awaken early in the AM, and sneak into the park before the Fee Collection boths are staffed. This is usually quite early, but it is worth saving the $20. Since you are up so early, you are the first to the crag, and don't have to wait in the normal lines on the trade routes! Works out pretty nicely.
Then you hang out in the valley, spraying at camp 4, or perhaps at degans, or camp curry, whatever, until late in the evening, when you high-tail it back past the now empty enterance check point, to your secret road just outside the park. I'm tellin you, this is the LIFE!
If you prefer sleeping in, you can pay your $20 entrance fee which is good for 7 days, which really isn't a bad deal.
Driving time from Hodgdon(enterance station) to valley is around 30-45 min depending on how many rental RV's you get stuck behind (yet another reason to wake up early), and how reliable your transportation is.
If you decide to try to park and sleep inside the park, you are a sitting duck. The long arm will catch up with you eventually!
good luck