If you need an interesting prototype for a small Post Office ...
... allow me to present the smallest Post Office in the United States of America ...
The US Post Office at Ochopee, Florida.
Just thought you might be interested in a for-real
RURAL Post Office ... It sits at the back edge of a clearing along side U.S.Rt. 41 just prior to Rt. 41 crossing the Everglades on the way to Miami. There are not other signs of human life visible from the location of the the Post Office!
For instance, the photo below was taken not very far from the Ochopee Post Office ... the area is decidedly rural!
Ochopee is so "rural" that the US Census Bureau has no available statistics on the area, nor does Collier County, the county within which it is located,
At least not that I have been able to find.
People in that area of the state pretty much keep to themselves, and don't appreciate being sought out by anyone univited, especially anyone from the government ... ... any government!