What year is your coach?
I would check the engine ground wire where it connects to the chassis. And then the positive connection.
You also have a few relays as part of your start circuit, but I'm guessing you have a ground problem.
The pictures below may or may not be representative of your start circuit.
Did you check your old batteries before you replaced them?
If you are capable, and feel lucky, you can alway try to bypass your starter relay, but you should be prepared to receive some sparks. The point is to locate your failed relay... if you don't fix your problem after making sure your positive and negative ground cables are ALL CLEAN AND IN GOOD SHAPE.