I've never used a grinder and only had a Sawzall to cut mine with. Used a 24 tpi blade and it cut the top like melted butta. It was pretty easy to keep the blade right flush with the side and made a real clean cut with minimal clean-up.If you feel more comfortable with the grinder it'll likely work real good too.
2004 Weber Performer GREEN
Orange Super-Duper Fast
'08 Weber Genesis Gasser
SJG Tamale Pot Mini Smoker (SJG was a rescue)
and a Pyro FIL