if you're just looking for it to make a nice air-tight seal, go to HD and get some weather stripping. I use the 5/16"wide x 3/8"thick black colored stuff when I use bare MDF boxes....really helps out with the seal, and it's only $3 for 10ft of it.
edit; Ben beat me to it. //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif