Hey Bob,
I recall reading that Weber does not recommend this. They reason that grease fires could occur. The drippings could be caught between the foil and metal of the cook box and start a fire, instead of dripping down into the catch pan.
Not sure if this is likely but I have a silver genesis where the drip pan just pulls out. Its easy and fast for me to clean nasty burned stuff with an old putty knife - being careful not to scratch anything.