Ext power
I think you know the answer to this and this is why we have Ground Fault Interrupter circuits to begin with. I would not trust the RV parks grounds or polarity and hope that you will not either. There was a story (and a lawsuit) regarding a GCFI improper pool installation and of course, a death occurred. I hope NO one gives you the blessing to do this. Just keep your loads down to no more than 2 high current loads and the 30 A circuit should have no problems as designed and built.
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