Yes but beware. High speeds might be an issue, also they can be stolen by deflating. Don’t leave them up there for long periods of time and careful with speed and wind. It’s generally not recommended but I’ve seen it done, stacking two might even be better than one. Boards like Red Paddle with the Stiffening strips are better suited for this. Monitor it closely until you know it’s limits, good advice for any roof rack and board mount setup. When it’s shaking and making noise you’re going too fast.