hi everbody, im hoping someone can help me here.

my wifes yeti developed a shoking leak with the panoramic sunroof and noone seemed to be able to fix so i removed the head liner to investigate. i fond one of the 4 drain pipes badly bloked and detached from the sunroof frame,allowing water to freely flow in unhindered. This was easily fixed but as a result the carpet and underlay had became badly waterlogged and because the issue went unnoticed for some time, things got a little smelly and after removing evetrything, a little mouldy in places.
the carpet underlay is easy enough to remove, however there is another piece i have to remove that is proving a challenge.
it is a heavy piece of foam with a rubber backing that appears to be a noise and heat barrier, and it runs up behind the heater fan box. i have removed the old one with just brute force, however , the fan box needs to be removed (from what i can tell) to attach the new piece once i order it. i removed he entire dash fascia but i am completely at a loss how to get the box out. do i have to remove the ENTIRE heater to get the piece out? or is there an easier way?