Call for Artists, Making Money at Juried Art Fairs, Craft Shows and Festivals
Seam seal will work fine on the inside seams of your KD. If it's one of the less expensive canopies, the top is not really waterproof though. Spraying it will help some, but the best solution is to get a vinyl top, like a Trimline or a LightDome. More expensive, but factor in how much time and effort it would take to recreate your work if it got ruined in a heavy storm.
I know, lots of of folks use the pop-ups. But they aren't nearly as bulletproof as the heavy-duty tents.