I've had no issues so far with my ZX-700 either. (Knock on wood.
My rig stays parked most of the time way up in the mountains so I added a power booster to the radio input (like the power input for the TV antenna that comes in almost all TTs now) and a handful of RF chokes everywhere I could think to put one. That did clear up some very minor hissing and helped reception some, but this unit is not going to get the reception we've all come to expect from our car/truck radio systems. The Concertone receiver just isn't of the same quality.
Personally, my only complaint is that the Concertone doesn't have any HDMI or fiber optic inputs or outputs. I read that they are working on adding those but for now my DVDs do not get HD, though the sound is pretty decent for a trailer. But we're supposed to be camping so what are we all complaining about!
As to the OP above...I'd say if you have any doubts about the Concertone and your audio system is important to you then get a credit for the unit and buy something that meets your needs.
And as for the salesman who might have told you a fib: I'm shocked I tell you! Shocked!
2010 Flagstaff 829RGSS
Still to go: AK, NL, NT, NU, YT