One recommendation if having a professional do the upgrade.
Have him put in a 50 amp outlet.. IF cost is a factor you can use 30 amp wires and breakers (for most "Home" sites this is more than enough power) but have him install a 50 amp outlet.
Two reasons:
1: Odds a professional will mess up a 4-wire 50 amp outlet: Very low (though I've seen it happen.. but this was not an outlet and the only damage was a couple fuses)
2: If you ever upgrade to a 50 amp rig.. No changes need be made.
OH and 3: The dogbone you use to plug in at home ... Can be used in a park with a faulty 30 amp outlet in the box (many of those out there).