I have posted 4 videos I made in a previous class regarding vapour barrier installation around an electrical box:
Part 1: http://youtu.be/_eT0wI7ElbU
Part 2: http://youtu.be/VqyE2JQUTDU
Part 3: http://youtu.be/4hitWqzcmOI
Part 4: http://youtu.be/Jdf4VsU5gRk
Please note that it would usually be preferable to use the “hats” (not the word that Montana uses!:)) that various companies manufacture for the same purpose as they are more durable, faster to install and easier to seal. However, this technique will allow you to make your own if you are in a pinch or if you have only one box to seal up in a renovation, for example.
The final result is the same – a continuous vapour barrier that is not compromised by holes or breaks. The strategy for a successful vapour barrier!
Think like a water vapour molecule!