Why I'm tempted to train for Rock and Roll Mardi Gras Marathon all on a Treadmill

Here in the northern Chicago suburbs it's freaking cold. According to to the Weather Channel's website it's about 15° F. Too cold for my tastes to run outdoors to train for Rock 'n' Roll Mardi Gras. I gathered a couple of clean water bottles filled two with water and two with diluted Powerade, grabbed 2 Power Gels, my iPod, and all my gear and ran 14 miles on a treadmill.  It took me a little over 2 hours to finish but I did it. I kept my self sane with my interval training, changing the setting on the treadmill, and messing around with the songs on my iPod. People running the indoor track said I was crazy. I can't will defend my self on that on can I?

I would totally prefer to run outdoors. If it's was nicer I would be running the trails at Busse Woods in Schaumburg. Unfortunately the trails are frozen and don't fully thaw until March. I would love to run the along the Chicago Lakefront but there would be no place to refill my fluids when I need to. I've tried running indoor tracks at my local Ballys Heath Club but I loose track of how much I run.  According to my running logic the treadmill is the most logical place.

Why I think the tredmill is the best place to train for my race:
1) Train me for the heat. From what people tell me it's hot in New Orleans. At least I'll be used to hot conditions.
2) I avoid the cold. I hate the cold. I think spring & summer can't come soon enough.
3) Because I want to see if I'm that crazy. I think that goes without saying. But why not just go all the way and see If I can keep my sanity for 16, 18, & 20 miles.

Some websites I've been reading said I should do 60% of my training outdoors. If I could, I would, but I can't.
I think that "completive, don't say I can't cause I can" part of me wants to see this endeavor come through. So in a few weeks I'll tell you how my 16 mile run goes.