The way I understand it, and I have not verified this is, is that 50 amp service is actually 240 volts. This gives you 2, 120 volt legs so to speak. Each of these legs is on an opposite phase. One leg feeds one AC and microwave and stuff, the other leg feeds the other AC. Each leg is only good for 30 amps each. Combined they will give you 50 amps total, (actually 60 on paper).
Now you can use transformers and boost voltage, but you can not boost current. If that was possible, you would have 15 amp service at your house and could boost it up to 200 amp. Then you could just have a plug in the yard and plug your house in like your camper.
Now if you are not confused enough, don't think you can plug in to the 30 amp service at a campsite, and the 20 amp service, and get a total of 50 amps. For one thing, this is only 120 volts, and it is only one leg, and therefore one phase, and the max out of that box is going to be 30 amps.
Hope I've not been too confusing. If all else fails, look at it this way. We have large wires on our campers to handle large currents. The power company has to use large wires to supply large current to our house, work place, etc. If they could use a smaller wire, how much cheaper it would be, and then all they would have to do is boost it on site. Believe me, they have tried to figure this out, and have been unsuccessful. The current is what you pay for, not the voltage. It takes big wire, big plugs, and more money, to supply and to maintain. Good luck.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT