Bobby, it isn't necessary to cut the pseudostem down. In fact, with musella lasiocarpa I did
not. I think you will find that the deeper you get into the colder zones (zone 7,6,5), the more pseudostem will die anyway, despite protection. If you were to leave a 6 foot pseudostem of musa sikkimensis, and wrap the whole thing, mulch, etc., in zone 6, and you were to have a true zone 6 winter, you would lose several feet of pseudostem anyway. Possibly the whole stem. BTW, I know you're in zone 7, I was just using that as an example
. Those in zone 8 (in the SE US) that grow musa basjoo and musa sikkimensis are fortunate enough to not need any protection from the cold in most winters. Last winter, I know of several folks in zone 8 (SE) that started out with over 10 feet of pseudostem on musa basjoo. I figure that they grow so dang fast anyways, that they'll make up for that 2 or three feet of pseudostem, that I cut down, pretty soon.
Taylor - I wouldn't even try to attempt that method with m. zebrina, and I'm not sure what s. lavender is. I would only bother with the really cold-hardy bananas. I use black plastic, as it heats up really nice, especially on those cold, winter days.