That's where I would put it since it will be easier to get to quickly.
One final thought, wear eye protection and a dust mask. The alum is not so bad but the powdered Hy lime is very caustic and smaells like pure ammonia when you breath it in. It can damage mucus membranes easily. Keep a jug of clear water handy to flush your eyes if needed. Tears will prevent eye damage, but it hurts like hell!
