30 amp service is USUALLY all thet is required for one AC, although if you have an electric water heater, and microwave, and try to run them all, some have experienced trouble.
Since this is a pop up. you need to be able to get a wire from the roof ac to the breaker box, and that wire must be able to expand and collapse with the roof. Is that possible? Then if you can, and it is a 12 gauge wire or better, smaller number, then you should be able to add a 20 amp breaker for the AC if you have an available empty circuit, which you said you do. Breakers should be available at any big box home improvement or hardware store. Pull one of the others and take with you to match it up if you have to. Make sure all power is disconnected before you do.
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