What is one thing another character says about him?
What does this reveal about
Holden's character?

Holden's narration is cynical and jaded, despite his intelligence and sensitivity. He finds the dishonesty and ugliness of the world around him virtually unbearable, and he uses cynicism to shield himself from the adult world's anguish and disappointment.

It shows that the camper meets all the author's travel needs.

Explanation:

The description of the camper in this passage is mainly to reinforce the utility of the vehicle. Every aspect of the design that is mentioned is practical and would a specific use on the road.

The author may be fussy, but ordering a specialized camper is not an indication of that. It is also unlikely that the author designed the camper since the specifications were sent to him.