If I read your post correctly, you are trying to get 50amp service to your coach from a 30 amp service pedestal. There are adapters that tie TWO 30amp plugs into a 50 amp and one that tie a 30amp and 20amp together to a 50amp. The first has two 30AMP MALE plugs to a 50AMP FEMALE plug and the other has a 30AMP MALE plug, 20AMP MALE plug and a 50AMP FEMALE plug. I think either of these are what you're looking for. That said, the 30/20 will NOT work if the 20amp receptacle is GFCI protected. New codes require that but if you go to older CGs they haven't been upgraded yet. They are not welcome in a lot of campgrounds also. Some specify you can be asked to leave with no refund if caught using one.... below is a link to one sold by Camping World and another form RVwholesalers...Dennis
Twin 30 to 50 adapter15/30 to 50amp adapter