This is total speculation...
It would be interesting to know which leg from the supply Main is furnishing power to the campers a/c unit... Since one outlet, of the three was working...could it be that it's getting line voltage from the other supply line?
In a house...electricians try to balance the 110 loads...to distribute the power drain from each supply leg. That doesn't happen so well in a campground perhaps. You may have 20 campers which drain much more off of one supply leg...and hardly any off the other. This will be exacerbated IF the gauge of the common wire is a smaller capacity than the gauge of the L1 or L2.
50 amp campers aren't wired to balance loads...they are normally wired to put as much stuff as possible on one leg...so that you can function when only a 30 amp pole is available...and throw the extras like second a/c, washer/dryer, etc...on the second leg for those time you have a 50 amp connection.
Anyway...I would ask myself these questions...
1) From the supply panel...have the electrician measure the amperage draw on each of the two service legs. Are they balanced?
2) If you trip one leg of the service main...and then check each RV service pole...is the remaining powered leg oriented to the same terminal? If so...it might help to balance the loads if you alternate... This will help to compensate for the way rv's use power.
3) check the wire gauge of the common return line. If this is less than the supply lines...then it can be restricting the service whenever the conditions enter an imbalanced condition.
This might be the problem. It doesn't mean that you have a bad electrician...just one that didn't think about how rv's are wired...and how imbalanced the loads can get when you have a bunch of them drawing power...primarily from only one service leg.
