That happens a lot. Mike planned for them to stay in a shelter, but much to his surprise the shelter was full. A huge group of Cub Scouts with an inconsiderate leader were already there . Shelters often fill up. Although Mike planned to stay in a shelter, a group of Cub Scouts with an inconsiderate leader had already filled this shelter to capacity.
Scout leaders are all too often inconsiderate of other campers.
Bill had been glad not to carry a tent, but now he wished they had one. Fine as is. It is no fun sleeping out in the open in the rain without a tent when it is cold enough to freeze the water in a water bag half an hour after it is filled up. When someone has just gotten back to sleep from the disturbance of wild horses stirring up Blackster the dog, it is unpleasant to be reawakened by heavy winds whipping the driving snow into the tiny opening of one's sleeping bag. Sleeping in the open in cold and wet conditions is not fun.