Well, I don't see where any one else has mentioned it, so do what I did. I used my Harbor Freight Multifunction Tool. That's the Fein MultiMaster knock off. You should be able to find a coupon to get it for $35. It does a great job and is available for a great many other jobs, since it really is a multifunction tool. It makes a little fine dust but there isn't any massive clean up required after you finish with the door.
By the way. You will probably need to cut each of the insert pieces in 2 so they will fit inside the channels around the side of the door panels. I suggest that you cut them on an approximate 45 degree angle. That way you can slip one half in, then the other and they will fit without having to be forced.
Bill