I am really late to this conversation.
We had great success growing them in delivered compost from out local farm store. We made 2 foot tall raised beds and put them in one end. They tried to take over everything. Grew like crazy and produced many wonderful sweet potatoes, even in our cooler Pacific Northwest. The raised bed was in full sun and it seems like the compost stayed very warm. Nights get very cool here (50 to 60 degrees), so I was pleasantly surprised to find that they were that easy to grown.