I have a fairly only PHD Minim sleeping bag. its the 400g ish variety with no zip.

I rarely use it, favouring my heavier and slightly warmer quilt. Mainly as I find quilts much nicer to sleep in, especially than a bag with no zip.

So, I'm thinking about modifying the bag. Basically stitching up a narrow Vee and thusly creating an enclosed footbox quilt.

Any tips before I have at it and ruin a perfectly good bag?

Did you bite the bullet on this?
Sewing with Down can be a nightmare.

Nah, bottled it.
Handled the material for a bit, decided I was going to ruin it.

Wise decision..