A window AC would generally have a standard 15A plug on it, and so is connected to a 15A or 20A circuit. It's not permissible by code to put a 15/20A receptacle on a circuit that has 30A overcurrent protection; it needs a properly sized breaker (or fuse) for the receptacle rating. You can, of course, have a subpanel fed with a 30A circuit and from it run one or more 15A or 20A circuits, which is basically what you find in a typical RV.
It is permissible per code to use wire that's heavier than the minimum required, but frankly for the distance between the power inlet in the RV and the window it's not of any real benefit to do so.
I think you would want a small 30A RV distribution panel (which may also have a converter and/or 12V distribution as part of the same chassis, depending on the model). There would be a 30A main breaker from the 30A shore power cord. You'd probably want a 15A (min 14 gauge) or 20A (min 12 gauge) circuit dedicated for the air conditioner outlet. You'd need at least one general-purpose 15A (or 20A) circuit for the lights and other outlets. If any of the outlets are near sinks or are on the outside of the RV, there should be a GFCI protecting at least those outlets--either a GFCI breaker, or a GFCI outlet. You might want to think about circuits dedicated to other high-power items, such as a microwave oven, water heater electric element, etc. Obviously some of those details depend on how the trailer is equipped.
The neutral and ground should not be bonded together in the RV panel; it's wired like a subpanel, not like a residential main panel. The electrical ground is tied to the trailer frame (whatever metal parts there may be).
