“Door to Door” "House to House” “Port to Port”

[Bobbert]

Many times I see “door to door,” house to house,” “port to port” written two ways:

puerta en puerta/puerta a puerta
casa en casa/casa a casa
puerto en puerto/puerto a puerto

Are they interchangeable? Does each construction convey the same or a different meaning?

However, I only see “class to class” written one way:
clase a clase (I have never seen clase en clase)

I sell my merchandise from door to door.
Vendo mi mercancía de puerta en puerta/puerta a puerta. (Are both correct? Do both say the same thing?)

I went from house to house looking for my lost cat.
Fui de casa en casa/casa a casa buscando mi gato perdido. (Are both correct? Do both say the same thing?)

They go from port to port every day.
Van de puerto en puerto/puerto a puerto cada dia. (Are both correct? Do both say the same thing?)

Now that I attend high school, I have to go from class to class.
Ahora que asisto a la escuela secundaria, tengo que ir de clase a clase. (Can “clase en clase” be used?)

I appreciate any help you can give me.