One pro is the uneven ground. I have searched the internet on under quilts for below zero and have found that the extra 2 lb some weigh is still lighter than a sub-zero bag with a top quilt. I would still be under the 5 lbs that a typical 3 season tent weighs.
Snow loads are a different story, I think a tent is a better choice and the 10 lbs my 4 season tent weighs would be okay.
