The most similar option we have to replace your Concertone ZX25 radio, is the Jensen RV Stereo # JWM60A.
This radio has a 3-zone output that allows for up to 6 speakers to be connected to the radio, and has mounting dimensions of 9" long, 6" tall and 5-1/2" deep.
I have attached a review video for you to check out as well. view full answer...