I really like a car seat we got. It straps safely in car with a seat buckle and we used it as a "crate" for potty training. It's big enough for a dog, but small enough so the puppy will resist the urge pee on one side of the crate and sleep on the other. I kept it next to our bed, and he woke me up once or twice during the night. I would place him on the pee pad in the bathroom, and then first thing in the morning, I took him outside. He became accustomed to using pee pads and going outside. Now that he's older, I use it when I take him shopping; as it fits well inside a shopping cart or you can just wheel it around. It's my favorite purchase. Here's a link, but I got mine at Target for much less.
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