R-19 should work fine but you have to use a thickness that will work in the space that is available. I have seen some opictures of restorations that have used foam board as well. Whatever you use do not pack it in too tightly or it will lose it's insulating properties.
![drinking](http://soda-machines.com/discussions/Smileys/smc/drinking.gif)
Tim
![drinking](http://soda-machines.com/discussions/Smileys/smc/drinking.gif)