Decoding a RS232 message in Arduino

I have an Arduino Mega with an MaxBotix (MB7066) sonar attached, the sonar has the ability to send serial data with it's reading. It uses a asynchronous RS232 format, except the voltages are 0-Vcc. The output should be a capital "R" (ASCII), followed by four digits(ASCII) and a carriage return (ASCII 13). The baud rate is 9600, 8 bits, no parity with one stop bit. What I get from the device is as follows: (sonarSerial.read() while sonarSerial.available())

43
192
6
6
179
89
30
0

What do I have to get to the information? Or is my sensor just retuning garbage? Please see the code below:

#include <SoftwareSerial.h>

#define pin1 3
#define pin2 5 //pwm
#define pin3 6 //analog
#define pin4 10 //RX for sonar, TX for arduino
#define pin5 11 //TX for sonar, RX for arduino

SoftwareSerial sonarPort(pin5,pin4);

void setup(){
   Serial.begin (9600); 
   pinMode(pin1, OUTPUT);

   pinMode(pin4, OUTPUT);
   pinMode(pin5, INPUT);
   sonarPort.begin(9600);
}

void loop(){
  digitalWrite(pin1, HIGH);

  digitalWrite(pin4, LOW);
  digitalWrite(pin4, HIGH);
  delayMicroseconds(20);
  digitalWrite(pin4, LOW);  

  long pulse = pulseIn(pin2, HIGH)/58;
  Serial.print("PM Result: ");
  Serial.println(pulse);  

  String buffer = "";
  sonarPort.listen();
  while(sonarPort.available() > 0){
      int inByte = sonarPort.read();
      buffer += inByte; buffer += " ";
      if(!sonarPort.available()){  
          Serial.print("Serial result: "); 
          Serial.println(buffer);
      }
  }
  delay(500);
}