I would be leary of any dealer who suggested that you were expecting too much from your converter and that solar was the prefered method. If it were me I would take the battery down to any tire/auto parts house and have it tested (it's free) - then check for an auto reset circuit breaker near the chassis battery, if that goes toes up it essentially disconnects the battery from the converter, test the converter by measuring it's output at the converter and while your there make sure the fuses on the converter haven't blown.
If the converter isn't putting out juice then replace - if it's putting out juice but it's not showing up at the battery then it's likely fuse/circuit breaker or lousy wiring.