Just a quick Heimlich update...
He's been living in his glass palace for four days now, and by my estimate, has more than doubled in size. He chows on milkweed, eating a leaf or two every day, and he's definitely eating more as he grows larger.
He is also a champion pooper, as you might expect from one who does nothing but eat all day. Caterpillar waste is called "frass", and you can see some scattered around on the bottom of the jar. I clean it out daily, because who wants to live in their own poo?
If you're worried about him getting enough exercise, you'll be glad to know that he sometimes takes a stroll in between snacks.
My guess is, at the rate he's growing, it won't be long before he needs to shed his skin. With luck, I'll be able to catch one of those molts on camera.
Keep checking back for Heimlich updates!