Porky Pig's advice is good. It is just what I have done to set pressures for my 02 25 ft Safari.
Since they are now using load range D tires, Airstream seems to have taken the easy road and is specifying maximum pressure on everything. I talked with Dave Schulmann, their service and parts guy, at Lansing last summer and questioned using 65psi on my 25ft Safari when it only really needs 30 psi to carry the weight. His answer was to use 65 psi. He had NO factual reason for his answer except that the higher pressure gives a safety factor.
I run my tires at 40 psi, so I have some safety factor without beating the trailer apart. The tires run nice and cool.
With a single axle trailer, it is even more important to not over inflate your tires as it has to have stiffer springs than a dual axle of similar weight.