Here's a picture of what I think they are talking about.
http://www.homeconstructionimproveme...insulation.jpg
Here's some further information on it.
http://www.ehow.com/how_4519628_blue...tion-size.html
I would put it on the outside of the tank and likely just tape it there so it could be removed if needed. Remember tape and snakes don't mix so make sure tape is never used unless it's outside the enclosure where the snake can never get at it.