This may not be the best solution for you but it will work. Buy a 240 volt breaker box, connect one load side of breaker to existing converter and the other side to your AC feed. Buy a new 25 or 30 foot 50 Amp cord and connect to the line side of the new breaker box.
If you can do it yourself it would cost $250 to $300, which would include the box, breaker, 30' cord w/ male connector, and misc. supplies.
You could add an automatic transfer switch or manual switch that would allow you to use the electrical system as it is now(incase there is no 50 amp pedestal)using the existing 30amp cord or use the new arrangement with the 50amp cord. Additional cost would be another $300 or so.