Your variables for controlling the temp on a WSM are, fuel, air and water pan.
You can run your WSM with a water pan with water, water pan with no water, and no water pan in the cooker. You can add more fuel to the basket to make the fire run hotter, and you can open the vents all the way open, or prop the door open.
You should be able to keep your WSM above 300 with just running no water in the pan and the vents wide open. Foil the pan in order to keep it clean.