Simple answer: With a 30 amp RV you are limited to 30 amps. YOU Can use a dogbone adapter and plug into the 50 amp outlet which may be necessary if the 30 amp outlet is defective,, but you are still limited to 30 amps. since that is all your RV can use safely..
You can snag an additional 12-20 amps.... Here is how....
Find the wire that comes off your main breaker panel to the Air Conditioner.. Disconnect it and remove it from the breaker box. if necessary use a junction box and additional wire to bring it to an area that is accessable from the OUTSIDE of your RV.
Install an INLET (This is a plug that is mounted in a box) at this point
Run a 2nd line from teh breaker to a pigtail with OUTLET,, SEE NOTE BELOW.
Get a device I'll try to link to (Below) I call a "Splitter" or Y connector. it splits 50 amp into two 30 amp outlets.. And you will need one more adapter to do it right but we can get around that easily enough. (Actually I'll tell you how to bulid it)
Plug most of RV into one 30 amp "leg" plug Air Conditioenr via the next paragraph into the other.
Building the adapter; You need a small box with a 15/20 amp DUPLEX outlet a 20 amp breaker or 120 volt fuse (I recommend breaker, a PUSH TO RESET kind is ok) and a short 30 amp male pigtaile
30 amp black wire to breaker, 12ga short lead from other breaker terminal to the copper screw on outlet, white wire to slivery screw on outlet, green to green.
Now using a 12 ga Extension cord.. I like to replace teh ends with 20 amp plugs and sockets (The blades are not parallel) use that to connect the the adapter you just made to the INLET for the A/C. Inlet can have any type of 20 amp conector either the perpendular blades or a twist lock.
the 30+30 to 50 adapter you need, DO NOT CONFUSE THIS WITH CHEATER BOXES which have two 30 amp plugs and do not work.
Amazon.com : Conntek RV Y Adatper Cord with 50 Amp Male Plug To (2) 30 Amp RV Female Connector (3-Feet) : Boating Shore Power Cords : Sports & Outdoors
Oh, alternate 20 amp adapter option.. Cut 30 amp end off the above adapter (one) and wire it direct to the box with the breaker and outlet.. NOTE: I do not recommend this cause some day you may need to switch legs due to outlet wear.