I have one of those cheater boxes.. MOST parks the 20 amp is in fact a GFCI and it will trip faster than you can say TRIP. Some parks even the 30 amp outlets are GFCI.. One park I stay at I check the box then go 1-3-4 till I find a pair of NON Gfci (the breakers are GFCI) One park has grandfathered 20 amps so no GFCI on a few sites.. but only a few. Those I like. 30 amp breakers on the 20 side too. AND.. I've seen the feeder wires (Long story but they failed when I was not there some years back so I got to see the new ones go in).. No danger of overloading park wires.. NONE. Zip. NADA.. manager said he did not want to have to do it again..> had to (one feed) less than a moth later but that... is another story.
Suggestion.. If driving REBAR into the ground to secure landscaping timber.. DO NOT drive into the nice just filled in line they buried the 240 volt feed in. Or the other wider one where they buried the new sewer line.. You won't be pleased .. Trust me. (NO I did not do that. but ... Well.. Today the guy who did... Laughs about it)