As far as charcoal smokers go, the WSM does about the best job of controlling the teperature. With most other charcoal smokers, there are issues with not having adjustable vents, not enough ventilation, or charcoal bowls that cause the coals to smother in their own ash. The WSM makes it easy to maintain temperatures for long cooks.
You should have no trouble on a 45º day keeping the temp in the cooking range.