I am a proud, unabashed FOILER! I have foiled my MAK since 2009. It is much easier to clean that way. When the foil gets dirty, peel it off, throw it away and replace. (Just be sure to POKE HOLES int he FlameZone ports).
I also foil my covers as well. Then once every couple of months, take everything inside the grill (except the firepot) and soak it in hot water with 2 cups of ammonia. Let it soak for an hour, then scrub it. Everything comes out really clean.
Even at GRILL setting (500+F), the foil is fine. So foil away! BTW, I used Reynolds heavy-duty foil. I buy the twin packs at Costco. About $17 for two of the widest rolls of foil.