What is it that you want 50 amps for? A 2nd AC unit? More power for electric heat? If so, as mentioned above, a far simpler and cheaper method is installing a 20 amp power inlet on the side of your unit somewhere and plugging into the 20 amp recept. on the pedestal. You could even wire it up so that you can supply more than one load like AC & heating (a SPDT switch would be one way to do this).
A 50 amp service may sound like a great idea but the 2014 NEC only requires 20 percent of an RV park to have 50 amp pedestals. Older editions of the NEC required far fewer - the '02 code for example only required 5 percent @ 50 amps. Unless you stay in a CG built after the 2014 edition, or at a CG/park where the owner went above min. code requirements, the chances of finding 50 amps can be slim to none in the high season. There will always be a 20 amp recept. by code. The NEC is way behind on the number of 50 amp RVs out there now. I've even seen a few high-end 50 amp MHs plugged into 30 amps with an adapter and then an extension cord hanging out a window and plugged into the 20 amp recept.