I took several pictures as I created the last batch, I missed documenting a few steps, but I think it should still make sense.
I started with 3 pieces of 3" wide wood, all a bit longer than the longest marquee I was planning to display. I clamped the wood together so that I could use one piece as a guide to route out a 1/4" groove.

I cut the groove all the way along all three pieces, leaving a 1/4" lip on the outside.

I rested the Marquee in the groove of the bottom piece and squared the side piece at the lower left hand corner, sliding the side of the Marquee into the groove.

Unfortuntly, I don't have a picture, but I then set the top down so the Marquee fit into the groove on the top piece, then measured it against the side piece, the bottom of the top piece told me where I needed to cut side piece. Once the side piece was cut, I put the remaining half of the side piece on the right side, to measure and cut that. This photo shows the end result; the marquee is in the grooves of the wood, sticking up a bit higher than the sides, where it would fit into the top's groove.

Putting the top onto the Marquee, I then measured and cut away the excess wood from the top and bottom.

Again I forgot to take a picture of the next step. Once the box was together, I clamped the sides all together and marked where I wanted to screw through the top and bottom and into the sides. I pre-drilled the holes in the top and bottom before assembling. I assembled it without the Marquee in place the first time, to avoid harming the Marquee.

I used a sheet of mdf for the back, I used plywood on an earlier version, but it splintered to much. You can see the screws in the bottom in the photo. I marked the back a little bit smaller than the size of the box, then cut it with a jigsaw.

I attached the back to the box's top and side, but not the bottom. The plan is to be able to open the box later by removing the bottom. (I have the bottom of the box facing away from the camera in this shot.)

I cut a hole for the cord in the back after attaching it to the box. I need to cut a larger hole next time, the plugs don't fit to well.

I used a little wood putty to finish off the top and sides, hiding the screw holes, the ends of the grooves and my non-perfect measurements. I did not cover the screw holes in the bottom. I sanded and repeated the patch job until smooth.

Now ready to paint, I used some Rustoleum gray primer first.

And then used black Rustoleum spray paint to finish.

I don't have a photo yet, but I bought some 3m self adhesive felt circles to put on the bottom.
Looking back on the finished product, I think they need another coat or two of black to really give it the right finish.
Thats it, I still have a stack of marquees left, so I'll be making more.