Hmm, most RV adapters I have seen adapt a 50 amp 240vac RV cord to a 30 amp 120 vac. I have even seen 50 to 20's for plugging in when at home.

Interesting if a 30 is plugged into a 50 which I have not encountered, but if so, you might be able to squeeze under the tap rules if the RV does have a 30 amp main.