Here's the radio location in a '89 2461, which shouldn't be any different except the bedroom area:
There's probably a hump inside that cabinet behind that panel. This should contain the other ends of the wires and provide a secure place to mount the radio. I think there might be a sticker on the hump inside. It should just basically be a piece of aluminum bent to cover the area, or it could be made out of luan panel.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR