How do I catch drippings on a charcoal grill?
The melting temperature of aluminum is 660C/1220F. It's extremely unlikely your grill will ever achieve that temperature. 

Although a rectangular pan doesn't fit a cylinder very well from a geometric perspective, in practice on a grill it fits just fine. Your food is rarely circular in shape either, after all. The Weber grills have a very good reputation as smoking/grilling devices. I wouldn't hesitate.