As mentioned, that splitter will do nothing in this application because it doesn’t combine the two 20 amp circuits. And it would be a death dealing device if it did because the odds are about 50/50 that any two randomly chosen and properly wired 120 volt outlets would be on opposite legs of a given240 volt service. This would result in an instant short circuit when plugged in, with attendant sparks and fire hazard. If one of the 120 volt 20 amp outlets was wired backward, you’d throw 240 volts on the camper instead, with equally devastating results.