If you're going to wear UA thermals, then why not buy a lighter pant that you could use during the warmer times of the year? I just bought a pair of Microtex pants from Cabela's, and love them. Been wearing them the last 3 or 4 days, with mornings in the high 20's to low 30's, a little breezy out, and they seem to be reasonably wind proof and warm. I am also a big fan of anything wool, love that stuff!
In regards to Carharts, I know that a lot of guys wear them, but I also know that in the survival classes I've taken, the catch-phrase is "cotton kills". I personally never wear anything cotton when hunting, because you never know what could happen while you're out there, so you might as well stack the odds in your favor, and prepare for the unexpected.