I used a fiberglass type blanket from my buddy's welding shop.
They use it to wrap weled flages to control the cool down.
Worked great, I was doing a prime rib and briskett for them for christmas.
It was 1 out when I started the cooker, got it up to temp and was adding wood every 30 min or so and running it hard.
Put the blanket on and within two mins the temp had jumped 5 degrees.
I was then able to run it like I normaly do even though it only got to 20 that day.