I built my KX1 along with the KXAT1 internal tuner and KXB30 30m module back in 2003.
I have used it a lot for portable operation, especially during the winter months.
I am a member of the QRP Polar Bears Group (http://www.n3epa.org/Pages/PolarBear.htm) ,
and we do a monthly QRP Field Day-like outing during the winter months.
I never go out of my way to try to keep the rig itself warm, only my external 8X AA battery pack
and I have never had any issues with the rig in cold weather.
This past Saturday I operated for about 2.5 hours with the air temperature at about
3 degrees F and the rig, including the internal tuner, worked perfectly.
It occurred to me that having an LED display rather than an LCD display was a really good
idea, especially for operating in these sorts of conditions and I am sure that Wayne must
have had this in mind when he made this choice. Also the DDS VFO is rock solid regardless
of temperature. Another big plus is the top-mounted controls, which IMHO are pretty easy to
use even with fairly thick mitts on.
Overall I think that this rig is unsurpassed for this sort of portable operating.
I use a Pelican 1120 Case to store the rig, my KDPD1 paddle. a Pomona BNC to banana jack adaptor,
my earbud headphones and a small laminated "cheat sheet" and I never have to worry about the rig
getting wet or damaged while in transit in my pack.