In reply to Ciro:
Wild camping is illegal on the beaches but you'll be unlucky to find someone pestering you this late in the year. That said, you should stick to remoter beaches and that means a bit of a slog from the car. The biggest problem will be finding a patch of beach that doesn't get covered by the tide. Such places exist but you have to know where they are, and know your tide-tables.
The majority of the car-parks on the peninsula are either NT or privately owned. There is no overnight-parking/camper-van parking spot of any renown on Gower, not even anything like the Mother Scaries car-park in Pembroke.
My recommendation would be to pony up for the camping at Pitton Cross or Hill End (if it's open).