Friends help each other out, hence she is helping me out. Silvia is one smart lady when it comes to this stuff and the ideas just flow from her mind. Her first thought was why reinvent what I already have, and she proposed adding a layer that can be attached to the existing quilt or removed when temps don't warrant it, plus the layer can do double duty in warmer temps as a single thin layer.
Next proposal was a rectangular sack to be used under the existing quilt. I will have to think about this as I don't like being confined in a "bag".
Then this popped into her mind, a dual fill, one layer down, and a second layer a batt. I told her about size constraints during storage on the bike, and she quickly ruled it out.
I'm sure she will come up with something.