Got everything assembled, for the most part.
Very basic lightbox made from scrap wood I had lying around. Couldn't really make it completely enclosed, since it's pretty tight on space, and it needs room for the buttons and whatnot when the control panel is mounted on the top. Will be lit with LED tape (drilled a hole to make room for the power cable). I was going to use a fluorescent bulb, but just didn't have enough room for it.
Found the retainer strip I'll mount above the monitor to keep the screen glass in place. It's just a 90-cent ruler from Home Depot, cut to size with screwholes drilled and countersunk. Also filed a taper on the top edge of the back, so it sits flush with the speaker panel above it.
It had markings and indentations on both sides, so I took my power sander to it. Should work just fine. It'll get painted black to match the cab.
Drilled some vent holes in the back. While I did this, I dropped the drill and took a chunk out of one of the MDF panels. So, there's another spot to patch up. I think I might put another 8" of fixed panel on the back before I paint back there. That way, the access door won't be quite so enormous (and I think I'll still have plenty of room to reach the components in the back.
Masked off the admin panel and the parts I'd already painted on the bottom...
And now I'm priming it. Using a spraycan for both sides of the front sections, with all the random nooks and crannies. It's crazy how rough MDF gets when you spray it with primer. So, lots of sanding to do. I have a gallon of Kilz and foam roller/brushes for the rest.
Ignore the bowing in the MDF below the marquee. You don't see that. And you'll see it even less once the marquee retainer goes on.