Just a quick update: I tried to cobble together a simple wood shelf with legs. That's pretty easy, BUT...with the shelf in place, and almost no matter how low or high I make the shelf legs, none of the grates will fit in. Why? Simple - the cabinet opening is 19.5" at the cabinet door. The grates (grill, main or upper) are just over 21". That means you have to angle the grates enough to clear the cabinet door opening. With a shelf in place, no can do, at least as far as my limited imagination and "engineering" skills can solve. So, my hokey little shelf is OK to allow more stuff to be put down there without stacking boxes or whatever, but won't allow the grates. The FZ covers will fit with a shelf in there, so there is still a good need for something that is more stable than what I did (1"x12"x"23" on 4 10"x2"x2" "legs"). My "legs" are loose - I need to cut the shelf down to less than 19.5" to have legs that are attached to fit through the cabinet opening. Of course, then the legs reduce storage space below the shelf even more.
I await the masters at MAK!