Without air flow it might rot.

That's what I'm worried about. I think I might have to drill some larger holes in the sides on an angle to keep water out and airflow possible.

Even in zone 6 in Michigan, I think you are wasting your time. With lows of zero to minus 10 degrees and the number of days you may be at or below freezing for sustained periods, it may be useless. How deeply does the spil freeze in your area. I would be more worried about saving the roots.

Sorry it took so long for me to respond. I really have no idea how deep the soil freezes. If I had to guess, probably about 6 to 8 inches. It can't imagine it freezes too deep, since here the weather is pretty extreme and definitely not predictable. One day we won't make it above freezing, and the next we'll be in the 50s. I'm growing Musa Basjoo, so overwintering the roots if kept dry shouldn't be a problem, as they're supposed to endure 0 F unprotected and down to -20F with heavy mulch. We rarely get below zero, but it may happen once a year. In either case, I do plan to mulch and keep dry with a tarp with all of my Basjoos, but my largest is the one I'll try to save the pseudostem. Worst thing that'll probably happen is the p-stem turns to mush, and the plant returns in the spring from the roots.

Last winter I got ~18 inches of pseudostem to survive the winter. Granted, we only went below 0F once or twice. We did have weeks at a time where it stayed below freezing though. Here's what I did: I cut the pseudostem down to about 2 feet tall, wrapped it in two layers of the pink roll fiber glass insulation they use for houses (ie wrapped around it twice), and then covered the whole thing with thick black plastic to keep water out. I lost the top 6 inches or so to freeze damage and/or rot, but kept 18 inches alive and healthy. There was no air circulation in there, so I honestly don't know if it makes a difference.

End of last summer:
{{gwi:406166}}

Wrapped, protected, and ready for winter:
{{gwi:406168}}

Me (6foot tall for reference) and my 'naners at the end of this summer: The 18" head start really made a difference!
{{gwi:422288}}

palmpunk, many people are overwintering basjoo stems in 6 or 6b.The most successful method seems to be the wire cage filled with leaves, and maybe something over the top to keepmost of the wet out.there is plenty of info if you do a search on this forum. some with pictures.

Yes, be certain to cover the top to keep water out. I tried burlap then 3 1/2ft of mulch and leaves then more burlap. I never covered the top to keep the water out. Come spring time all I had was rotten mush. Even the roots were rotted. I was sooooo stupid. This year I'm trying the large garbage can method stuffed and well covered. I did this on wednesday 11/08/06. Now, it's been so warm here in NJ(higher 60's) I'm worried their cooking inside. My back up plan is some in my crawl space under the house and others in pots in the den. I'm planning on winning the battle this year either way. Dan