Yak,
You can get replacment heater channels at your local VW parts house. If they don't have they can order them. Or pick up a copy of Hot VW's. There are many advertisers that carry them.
And a video onhow to do it here:
http://www.jcwhitney.com/autoparts/P...X/appId-311297
I would hate to see you scrap a perfectly repairable car because of rust. I did the entire pan halves on my car. It is a lot of work, but it is worth it knowing that you saved a Bug from the crusher.