bxowner, my parents have the JD Soft Side Cab, but its on a older 425. To me it looks like what JD calls a weather enclosure now and what you guys are all looking/talking about. It has the fiberglass top and steel corner posts (sheet metal) and then all vinyl doors, and windows. The only glass is the front windshield. In all my years when I was younger living at home, it never once fogged up on me. It gets a little chilly in there if you are in for a long time, nothing bibs and a winter jacket can not help, but you are not getting wet and having the wind blow in your face. In my opinion it works great.
I just put a hard side cab on my tractor with a Tuck A Way Heater, which made me think it would fog up so I also but a defroster on the top of the cab blowing down on the front window for the just in case factor (Didn't want to find out the hard way in the first snow blowing). I have not used it yet, I'll just have to wait and see how it works.
P.S. I got the heater more for the wife then me. In a cab its really not that bad. Figure make the wife's life a little easier when I'm not around to take care of it.
Also every dealer I talked to, said not to get the electric heaters. Something in the manner that they don't work real well or last.. I don't remember.
Hope this helps.
Dude Man