Alas, a Saturday night in the middle of Summer is not the best time to find camping close to a large metropolitan area. Try the California State Parks website (www.parks.ca.gov) for State Beaches and the few nearby State Parks that offer camping. There are no National Forests within an hour of SF. County and regional parks are an option but my guess is they are full this time of year. I have no knowledge of private options.
You will probably have better luck on Sunday, but even that may be problematic.
Parking in SF can be a huge hassle even in a compact car let alone a full-sized pickup or larger. Consider parking at a BART station in the East Bay or on the Peninsula and taking BART into the city. Marathons attract a lot of people so prepare for a walk to get to the event. Your friend, if from the Bay Area, can provide much guidance here.
Sorry to be such a "Debbie Downer", but it's crowded here.
Alan