anyone ever use one of these in combo with a pad?

I have a closed cell thermarest as well as a "self inflating" thermarest and i was thinking about adding one of these to my set up for my upcomming winter road trip. right now i have a WBBB and i use my thermarest self inflator but i havent been below 30 in it yet. will be hitting grand canyon, new mex, tex, colorado and utah in dec and jan, most nights im looking at teens to 20s. think adding one of those would be worth it?
also with the double layer WBBB, should i put it directly below bad, or in the sleave with mat?