When we picked up the GS from the factory they told us to foil. I have done it since day one. So far I have not noticed any temp swings, I use a Smoke to monitor pit temps. When I do a cleaning I will put 4-5 layers on the drip pan, when I need a clean one I just remove the top layer. The commercial aluminum foil from Sam’s is thick and wide enough to wrap around the sides, no problems at all with grease getting under it. Reynolds brand is a different story, it’s thinner and not as wide, always had grease under it.