You can find disposable aluminum "mini" or "half" loaf pans at most grocery stores. It's normal for the temps to swing above and below your set temp if using the built-in controller. It's not an issue for most things, the temps will average out and your food will cook fine. When my #1 was new, I had larger temp swings like yours. Now that it is well seasoned, seems like the temp swings are smaller. I don't even bother to measure the box temp anymore for things like brisket, butt, ribs, chicken etc. After several smokes, the box temp was pretty predictable to what I set it at. Now I only monitor box temp in cold smokes.