If you have the time to put it in a socket, that's probably your best bet. There are many diagrams and pictures of various incubators. Some have thermostats to control the temperature better.
One of my mother ducks was attacked and eaten by coyotes about 3 days ago, so my incubator is a very last minute sort of thing.
I grabbed a foam cooler, packed straw into the bottom, cut a hole in the top for the lamp, and put a thermometer in with the eggs.
The eggs are most likely past 3 weeks, so I don't have to worry about the temperature being exactly spot on. I have some rags with water in there for humidity.
Seeing as they went an entire day until I realized their mother was no longer on the nest, I think they will pull through. All are still alive and moving when I candle them.
They are Pekin ducklings, by the way.