I'd be careful about putting any metal other than aluminum in an aluminum tray with any kind of electrolyte. It could create its own battery and eat holes in the aluminum, causing quite a mess.
I used to take a frozen meal to heat up at work. Could be spaghetti or stew in a steel bread pan. I'd cover it with foil. By supper time, the aluminum foil had lots of holes in it. The ions (salts, acids, etc.) in the food created a circuit from pan to food to foil to pan (by direct contact) and merrily transferred aluminum into the food. Yummy. Putting a layer of plastic wrap between the food and the foil solved the problem. Lining the aluminum tray with wrap so the steel never touches the aluminum should work. Doesn't even have to come up the sides.
Bill, check your pan for leaks and let us know. I, for one, am curious.