I'm new to HF and have searched the DIY section but can't seem to find an answer to this question. Sorry if it's been covered somewhere already.

Has anyone used one Costco down throw with an added sewn on layer of Climashield and nylon? If yes, how did it work for you? If no, how do you think this would work? I'm going to be hiking the North Coast Trail on Vancouver Island in July. Nighttime temperatures can get to 9C (48F) but if a storm is blowing it could get colder. I'm worried that a one CDT as an under quilt and one as a top quilt will not be enough.

I'm an experience sewist so I thought of adding a layer of Climashield and nylon to both the UQ and the TQ to increase warmth. Would the added layer just crush the down making it less warm? If you thought this would work, which layer should be next to me on the top quilt and which layer should be closest to me on the under quilt? is there something else I can do to up the warmth of the quilts?