OK, I believe your original question has been answered. Three wire 240VAC, NO. Four wire 240VAC, should be fine. If it's a four wire, measure to make sure: 120VAC between each hot and ground/neutral, 240 VAC across the two hots. Or if you plug in your dogbone, you should measure the 120VAC between hot & neutral, near 0VAC between neutral and ground.
Now, if it IS a three wire, and you or your cousin are comfortable wiring up electrical things, you can use the wiring to that outlet if you change the breaker in the panel to a single pole 30A unit and change the receptacle to the 30A 120VAC RV outlet. That will enable you to use that outlet for your 30A service while you're visiting. Then when you leave, you can rewire it the way it was.
~Rick
