Before you fill your new planter, our friends over at Shelteriffic suggest wrapping a layer of bubble wrap around the inside of the container. It will create a small barrier between the heat of the metal walls and the tender roots of your plant. Even though plants can take a little abuse, there's no reason to make them have a harder time staying alive!
We think it's a great tip, though you'll need to make sure you buy a pot large enough to give your plants' roots room to grow, since its new home will be slightly smaller. Although it sounds a little odd, it should help plants that dislike heat (cilantro, anyone?) or the super heat that metal pots can cause!