There are many templates for making your own envelopes. But instead of downloading one, printing it, trimming it, etc. etc., I carefully opened an existing envelope and there was my template. No trimming needed, either.
So here's an envelope made from scratch: the envelope itself, made from kraft paper that I stamped; the label (one of my collages, turned into a black and white image, and printed); and a little house I carved from an eraser.
For Jc and anyone else interested:
Be good to your friends -- Kevin Bacon.