according to your avatar, and your machine info, you've already got the heated tube option.
I have that unit, and I have no rain out issues, have you tried turning down the humidity a bit, and placing the machine just a bit below where the mask height is? Just trying to help you if I can.
If everyone thinks alike, then someone isn't thinking.
Everyone knows something, together we could know everything.
I purchased and installed the heated tube upgrade myself. If you still need to know anything just post back and I'll try to answer. I love the heated tube over the non-heated one by the way.