Need help adding a transfer switch

I appreciate all the help here. I think my question got off track or misunderstood at some point. Lets try this..... The picture below is my 3 wiring options for the Onan. Again, once I get to the transfer switch, I want only 1 120V line coming out. I need to be sure I'm actually utilizing the generators full load capability because at times I may be pulling up to 30 amps out of that 1 line. I know if I do this wrong, I'm really only using one circuit on the generator and only that one circuits breaker will trip on the generator if I overload it.