To check airport's short-term and long-term parking availability, call SFO QuickAID courtesy number (650) 877-0227. Off-airport long term parking information also available at QuickAID.
If there are no compelling reasons to drive, I'd recommend the use of public transportation or van service to the airport. An inexpensive way is to use Super Shuttle. You can make a reservation online. It is very inexpensive (about $20-30 from the peninsula) but you may end up being at the airport much earlier than you need to. The pick up time is 2 hours before flight time. Private limousine or "towncar" service runs about $50. Sometimes private limo service is better if you have 2 or 3 people travelling together.