If you have a 50 amp circuit, you should ONLY be using a 2 pole 50 amp breaker. NEVER use two single pole 50 amp breakers. The circuit is rated for 50 amp max.. Also larger wire are multi strand and extension cords use a larger number of strands per wire size to add flexability to it. The more strands also helps increase (slightly) the current carrying capacity since it reduces the "skin effect" of AC current flow.
Now, a single phase 240 volt system with neutal is 2 120 volt circuits IN PHASE with each other. This is called a split-phase system and is the norm. in the US utility system for single phase usage. If you have 5 amps on one and 4 amps on the other, since they are in phase, the neutral has 1 amp on it. They cancel out eachother and the resultant is what is on the neutral. This why your neutral wire (in your panel) is half the size of the main conductors. A 30 amp circuit (RV) is a single pole 120 volt circuit only. The 30 to 50 amp adapters connect the 2 "hot legs" of the 50 amp plug together so the 30 amp circuit will supply power to the unit HOWEVER you will need to reduce your power draw. Hope this helps.
PND
45 years in electrical
Marine and High Voltage Jouneymen cards
Utility Relay Electrican