Under-dash insulation falling down

I've got my rebuilt heater box back together and was about to put it back in the car when I noticed the under-dash insulation has fallen down. Looks like the adhesive let go across the entire piece.

I'm thinking I should pull it out, scrape off the remnants, and replace it with Dynamat. I can use the old insulation piece as a template for cutting the Dynamat to fit.

Any better ideas?