never thought about the heat aspect but will be doing some testing soon as holiday after tomorrow and some vegan bbqs planned my ex converts old plumbing things, big pot a tank again in copper, and I did the other round one, basically an old sink, I'm a tight git, top is
Copper fountain ex plumbing scrap converted to solar power with a cheapo ebay set, works great
Testing aside, it's going to roast your rear if you sit on it, literally... if you want to keep with the metal cover it with something so the sun isn't hitting it directly. I'd think that metal plant pots aren't going to do the root systems for your plants much good either if they're sitting in direct sun all day, unless you've lined them with something.