Being a '94, do you have stickers on the ceiling indicating where there are speaker wires? There might also be a sticker where the pre-wire location is for the box of the unit. I had a '94 2251 and it had those stickers since it had no radio from the factory. In the late '90s, Sunline did put the radio antennas on the roof, but for '94, they were mounted in the sidewall, usually on the opposing door side near the front.
For a 1550, I'd say the radio would probably mount in the cabinet over the sink/stove, or on the side of the cabinet, either upper or lower (by the door)
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