Heater Channels and rust

So i have really started getting into working on my beetle over the last few weeks. It currently has everything on the floor pan removed (carpet-rotted, underlay) incl rear seat etc. I originally decided to do all the rust work myself, sanding it back, then going over it with KBS. I thought i would be able to make quick work of this. However, in some areas of the car, light wieght placed on the metal is causing the metal to flake and bust off (passanger, top corner footwell mainly) .
Overall there is lot more labour work involved then i originally thought (no i am not giving up). On the inside of the car, on the rear arch's, there is a sticky material (how the orginal underlay was stuck down i presume), how can i remove this?

I also seem to be having some grief with some 40+ year old bolts. Grr

I have also have noticed now that my heater channels inside the car are not in the best condition, and i would like to replace it, however i am having trouble finding some of the parts on the net.
I have found:
The channels themself on multiple websites
Floor air vents for driver and passsanger
Hoses, tubes, etc.
But now i am having trouble finding what i call" the heater with holes and foam around it part". What is this? Where can i find it? but most of all, what purpose does it serve?

With the heater channels themself, i have no clue how to remove them.

On a side note:
I will be investing in John Muir's-Idiots guide to keeping your VW alive.

Jeremy

For John Muirs book, you can go to The Book Depository online in UK.

They have the book for about $30 delivered to your door.

the ones under the rear seat?
i might have a spare set from a 72 sbug if the will fit.

what i call" the heater with holes and foam around it part". Yes, that is the bit under the rear seat, ill take some photo's. I really got stuk into hand sanding things back to bare metal since i posted this thread. Need to purchase a wire wheel to have a good go at this. New heater exchanges arn't cheap -_- but if new ones are needed, ill have to get them.

Heating systems aren't cheap.

ill check with the old man see if i still have the pair and if they fit a 70 bug

what did your old man say barls?

hes away atm, something even i didnt know. gets back on wednesday and will have a look then.