It would be helpful if YOU posted a picture of what your setup looks like. It really shouldn't be too hard. Find a way to bolt the unit down. Run the wires through a hole in the back or bottom of the glove box and wire it all up.
It really isn't that hard. I like to use light aluminum sheet to make the mounting plate. Besides being easy to work with, it look wicked when polished. If your opening is rectangular it is that much more easier.
In my 56 merc (the easies to do so far) I made a flat piece and bent the sides, top and bottom 1/2" back to create tabs to screw the plate to the inside of the glove box opening (the box and door are separate here so the entire box could be taken out and I still had the door to hide the deck). Cut a hole in the plate for the deck and that was it.
In my brother's civic, we made a flat plate that fit snug into the plastic box (door and box are one unit here, as with most new cars). Drilled and mounted a couple angle brackets to the inside of the box and then used 3M double sided trim tape to hold the plate to the angles. This box was so small that we had to cut a large portion of the back out so the deck would fit.
I think this is a great idea to keep those thieves at bay, and it cleans up the dash a lot. Sorry I don't have any pictures but, with some tinkering and trial and error you should be able to make it work.
In my '64 caddy I just got one of those plastic under-dash boxes, flipped it over and attached it to the floor of the glove-box. I had to cut out the back of the glove box for clearance.
It looks like it came that way and I just put a modern stereo in.