I don't have a hot box here. Maybe it's our climate, but they never seem to work for me. If I had one, I would allow my sweet potatoes to seed, cut it into small chunks, root them and place them in the hot box. Instead here is what I do.
Before digging up the tubers, I cut the leaves off at the base. The ones closest to the mother plant. Cut at an angle like you would when cutting flowers.Once that is done. Bring them in the house and set them in water.
After a few days, roots will develop. These need to be placed into a large flower pot of good soil.
repeat the process in the spring, instead of planting them in the pot, they are ready for garden planting.
We had our first freeze of the season this weekend. I will start doing more indoor things shortly. I should also warn you, we tend to lose electricity, if you have to heard from me for a few days, this will be the reason.