So, I am having a party this weekend and using wire chafing stands with sterno to keep food hot. I am ordering all hot trays and making a few myself and using the large size pans. Do I need to buy a second large pan to put water in and then put my pan in it? Wont the water be pushed away? I heard I am supposed to use half trays, but the food I am getting catered comes in the large ones. Tips for keeping hot?