I found a nice deep frame in Ikea, though it's designed to hold a picture at the front, so it required some modification. Here's a photo of the frame with the glass and mat board clipped down.
Once that dried I trimmed the edges.
Then came the turn of the glue-gun. It might have been wiser to practice more, but I totally got away with it. The glue gun stuck each part fast to the surface below it.
Next, I needed some spacers to hold the back at a distance from the mat and glass. I have been saving almost all of the cardboard that's come into the house for several months now, so I was able to just cut some pieces of nice thick cardboard for the purpose.
I was very haphazard about cutting out the pieces, but they worked out fine. They're also glued on with the glue gun. Possibly overkill, but I had it right there ready to use.
A little black poster paint, in case the viewer should get an angle where the spacers become visible.
For some reason, I've only ever seen masking tape hold backs on pictures. I don't know why that is, but I didn't see any reason to break with tradition. It's not terribly neat, because the only masking tape I have available is a very wide roll, but then again, it is the back.