Here is a cool tent that lets you add a cabin to your paddleboard. It simply uses your SUP board as an air mattress.Two sidepipes are available to make the board and tent very stable on water. You can use this on the roof of your car. You can also use it as a trekking tent.
The BAJAO Cabin fits boards 11.2ft and above. The tent is 3 meters long and adjustable to boards of various width and length. You can find out more here.