[Fulltiming]

I pulled out a 30-50 amp pigtail that I carry in my coach and ohmed it out. The only difference between the wiring on the diagram you originally posted and my store bought pigtail is the white and black wires at the 30 amp end are reversed. On mine the white wire (neutral) goes to the 30 amp blade on the right rather than the left and the load line (black) goes to the 30 amp blade on the left when looking at it from the blade slide. The load (black wire) would connect to the two center blades as shown in 50 amp receptacle of their diagram. After I checked the continuity, I noticed that the male and female end of my pigtail are marked with a G on the round plug and a W on the blade above and to the right of the ground as my testing confirmed. The diagram you referenced would reverse the polarity which in most cases should physically work but would be a safety hazard and a code violation.

Since you are starting with a 30 amp 120 volt source, the pigtail is never going to give you 240 volts. All it does is give you the correct receptacle to plug the 50 amp plug into and provide the 30 amps to both 120 amp circuits in the coach. Remember that the 30 amps is the maximum load you can put on the two coach circuits combined (ie 20 and 10, or 5 and 25, or 30 and 0, etc.).