I have a couple of electric warming trays. I tried using them for Christmas Eve, and only got so so results from them. But I am sure I am not using them properly. I am looking for tips for using them. Do you put pans directly on them, or do you use some kind of water batch like a chafing dish? My newer one came with a frame and metal pans, but they stay about 3/4in above the tray itself, so I am not sure that is functioning properly. What temp do you usually set yours at?