How is the kayak sitting on the cart - how much of the hull is supported? I don't know anything about your particular kayak or cart, but I'd be cautious about leaving a boat sitting outside in summer heat in a position where its weight is supported on just a small area of the hull bottom. With some plastic hulls this might cause warping. Don't know if this would be a problem in your case, but it is something to consider.
Wall Mount Boat Racks