the best deal in solar tiles to cover your car and offset the parasitic 12vdc loads is these 22.5% efficient semi flexiable laminated panels, glued down with self leveling rv roof cement or high quality UV stable greenhouse repair tape:
18v 18w solar panel semi flexible charger & usb for Battery Caravan Camping home | eBay
when shopping for your pay attention to the wire output bump, you dont want it on the bottom, and you dont want it to be great big with oversized wire, think petite....