Heat grill to medium-high (350 F). Soak corn in water for 10 minutes. Place steaks in a shallow dish and pour 2 tablespoons barbeque sauce over steaks. Turn to coat and let stand 10 minutes. Toss squash with remaining barbeque sauce. Place squash and chopped rosemary leaves in a vegetable grill basket. Place steak, squash, and corn on grill. Grill for 15 minutes or to taste, turning steaks and corn after 8 minutes. Stir vegetables frequently. (Corn husks will be charred.)