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Hi Klepto,
You can use a couple of pieces of damping mat for the smaller holes //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
.A curved Punch Hole is difficult....But I believe you got the right Idea on the sheet metal.Of course you know you'll need to fasten it with "Short Self/Tapping Screws".
You should use like a construction paper and a Sharpie or Pencil to make a Template of each of the big holes...Trial Fit...Trim Maybe..Re-Fit.You can than use the sme templates you used on one door...flip it around and use it say...on the Pass. door.Make sure you leave enough sheet metal around the holes to allow you to screw that to the door skin!!!.You have to watch where you put the screws...Wires/Cables/Moving Parts/etc.And "Poke Small Holes" thru the paper,and mark on the door skin where you want to put the screws.Take A sharp metal punch or awl,and where you made the marks on the door skin..Strike the punch w/a hammer to make a dimple in the door skin.I would in that case drill a small pilot hole into each dimple to make sure the screws "won't drift.Dill Holes in the Sheet Metal piece Before you silicone it.This will make it easier for you toThen you Trace it out on the sheet metal.
*The Amount of Time* spent on doing this Depends..."On You".If you take your time,which you should with the sheet metal,It's tedious...Believe Me...but The rewards will be //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
.If you can...use 2 or 3 layers of matting(Depending on Brand and your Budget) on the inner door skin.You can do the outer skin...but that's a big help too.
On my 1989/Mustang-GT..I used 1/8" Flat Aluminum Plate to seal the punch holes in my Door Skins.It wasn't an issue w/moulding or anything...'cause the holes were all flat..Thank God!!!!!!.But cutting the aluminum was a real Biatch to do using a milk crate and a Jig Saw .But I did it....and put 3-Layers of Matting on each inner door skin.
All The Best With Your Project....and remember...*Patience IS A Virtue*.
Kind Regards/