rooftop cargo box (Alameda, California)

Hello everyone! My partner and I are currently in the safe parking program in Alameda and are wondering if anyone has a rooftop cargo box (hard-shell cargo box or even a soft cargo carrier bag) that could fit on our racks. We are currently sleeping in the car and we could probably fit back there if we had someplace for our clothes and food. Thank you in advance if you have any leads or can help. Mahalo!