Burrow + bivy bag

I have a 3 season burrow on order, and I'm trying to think ahead. If I have to go to ground, would the burrow work inside a bivy bag, or would the loft compress too much? I thinking an eVent bivy bag, lightweight.

Also, if it's really cold, would it work with a burrow inside a bivy bag, and a Mount Washington 3 on top of it all?

The burrow is rated for 15 degrees, and the bivy bag should give me another 7 degrees, plus an MW3, what, another 10 degrees?

Or maybe both burrow and MW3 on top of bivy bag?

I have an Exped Downmat 9, so bottom insulation is not an issue here.

Any thoughts?

The Exped is thick, so it'll probably have to go outside the bivy to keep from compressing the quilt inside a bivy. That means you should have a groundsheet to protect the downmat, and that you might lose a bit of heat from the pad b/c the wind will be blowing over the top of it.

Still, if you sleep on top of the pad and have the burrow inside the eVent bivy, you should be warm on the ground to some pretty cold temps.