And now, let's go after this lovely bunch of holes:
First step is to cut access holes in the outer three layers:
I found this little surprise inside the first layer. You can just see it in the bottom of the hole in the above picture. It's one of the bits that was hole cut -- it fell inside and was left there. Unfortunately, it's useless as a patch, so it goes in the scrap bin.
Second layer access:
The cut pieces for the first two layers will be saved and welded back in later.
Then, the third layer.
Once I got a little further into making the patch for the innermost hole, I realized I needed to make the third layer hole a little larger. I'll just make a larger patch later.
Now it's time to make a patch for the innermost layer, the heat duct tube. This is the masking tape method. First, put masking tape over the hole:
Then, use an x-acto knife and cut out the tape over the hole:
Remove the cut piece and place it on a piece of sheet metal:
Then, cut out the piece of sheet metal, and you have your patch:
Since this patch goes on a tube, I found a socket that's about the same diameter as the tube and shaped the patch over the socket.
