My lives under a smaller covered porch. I have the silicon mat thing and a water resistant cover over the whole thing. The mat and/or metal cover in my mind is needed just to keep dust, dirt, schmutz, bugs, etc off. Before I added the mat, even with the overall cover there was always stuff on it. Don't think you need both metal and silicon.
Mine sits on an Amazon brand X cart and the big cover is also to help keep that thing from rusting away as fast.
Get the little foil loaf pans to line your drip tray with. Easier to toss than cleaning that thing out. And always keep a spare tank on hand.