If you stick with the 13.5k a/c and don't anticipate ever changing that nor moving to a bigger a/c, then 30amps should be fine. Nevertheless, I'd go 50amp because it would give me flexibility down the road plus it lets you run a bunch of things at once (a/c, micro, hair dryer, elec water heater) that would trip a 30 amp.
More important, I would go with a 15k a/c. I believe the upgrade, when I ordered my trailer a couple of years ago, was $150. I don't think the difference in cooling is huge, but it's there and worth the small premium.
FWIW, if my a/c starts while we're running the microwave, we'll often trip the breaker (30A). It doesn't always happen, so I'm thinking something else is running when it does...probably the water heater element.