Tom N wrote:
110v 30amp yes
220v 30amp NO
Installing an outlet just for an RV, unless its a specific install with no other possible uses, is not wise.
If you want to install a 220v 4 prong twistlock (NEMA L14-30P) outlet, I highly recommended it. You can easily use a dogbone adapter for RV use.
IN FACT, I have the dogbone on board the trailer at all times in case we need to use a generator for power. Generators with 220v outlets use the same 4 prong L14-30P twist outlets. And you can still draw 30amps, as the wire size is still appropriate for 30 amps when done to code.
http://www.amazon.com/Camco-55382-Generator-Power-Dogbone/dp/B0024E71BQ/ref=pd_sim_sbs_auto_1