Voltage any where in the trailer should be good enough to check for 30 amp service. For 50 amp, you would need to know that you are on the same side of the 240. If you’re getting 110 or above, you’re probably OK. What brand AC is it? You should check amp draw of the compressor to see if it is working hard. Also, as mentioned, you need to make sure that the divider board in any brand is foil taped very well. Also, pull down the ceiling vents to make sure that they aren’t leading cold air into the space above the ceiling—may need to add foil tape at the vents to prevent leaks.
Just got down doing all this and still had a problem cooling on a 90 degree day in full sun in IN, not TX. Turned out that AC was bad—it happens. Got a new one, and what a difference.