Those who have tried using an insulated air mattress in their Clark NX-250, TX-250 or similar please tell me your experience. I have a new clark tx-250 and I'll be taking it out this winter up in the mountains of eastern NC early in December. I would expect the night time temps to be in the 20's but it could be warmer or colder. I have a regular size REI stratus pad which has an R value of 3. I know an underquilt may be a better option but I don't really want to spend the extra money right now. I don't want freeze either and thats why I'm asking.