I made one out of wood, and painted it black.
Just 3" high, and large enough to just fit in rear cargo area, on floor, works a treat
Like a small podium, approx 3' square, my jeeps at menders, so can't measure, wood cost around £3
Paint, matt black, almost invisible from outside.
Similarly, I made a tonneau cover out of dowel, and black fabric.
Dowel just fits in receptacle, total cost around £5
BTW, when I bought the 94 Cherokee, it came without radio, bought £30 manual FM /AM & cassette from local car spares shop, works ok, but has the added bonus of having 3.5mm jack input on front, for CD / MP3 player, brill