The wiring setup you want is the middle one in ScottG's post above. It uses BOTH hot legs from your house panel. The one on the left is only 30A and the one on the right's sometimes called "Fake Fifty" since it powers both terminals from only one leg, like the 30A.
The "puck" adapters really do burn out easily. I've never cut one apart to see how it's built. My thought till that explanation came in was... The Prongs get hot at the wall socket, and the Terminals get hot at the RV shore tie Prongs. The two sets are so close together the puck can't do much but get hot and burn out.