I put my hand under the plastic of the tomato greenhouse this afternoon and it felt very warm. I think this might work very well.
I decided to put bricks all around my plastic bottle greenhouses over the two peppers and eggplants to help retain heat.
Thankfully, I did not repot all my eggplants for the front porch, so I only had one to bring in! I would not have had room for all those big pots. But the seedlings seem to be happy staying in their little 4-inch pots for the time being.