It's still 1-2 months from the time I need to over-winter them because I want to make sure they don't continue growing after I cover them up. I usually wait until November. Here's the steps I plan to take.
1. Shrink wrap the P-stems after cutting the leaves off to make sure that they don't get rotted by too much moisture.
2. Place a 55 gallon plastic barrel which has a hole through the bottom over the whole thing.
3. Stuff the barrel with leaf mulch.
4. If there is more P-stem left, repeat steps 2 & 3 with another barrel on top or a trash bag.
5. Seal the top with a trashbag ensuring moisture doesn't get in.
6. Shrink wrap the entire set up to make sure that it doesn't allow moisture to penetrate.
7. Tarp over everything for even more insulation.
Here's the same exact set up performed by someone on youtube, but they using slightly smaller barrels.
Overwintering bananas - YouTube