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

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

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.

I don't know in other regions, but for this activity of going from one place to another, I prefer "de puerta en puerta", "de casa en casa", "de puerto en puerto"...

I don't know how to explain the case where "a" would be used instead, but here are some examples:

- Puerta a puerta, todas se me han ido cerrando y no encuentro la salida.
Every door has been shutting down on me and I can't find the way out. (Each time I saw an opportunity, it was cancelled before I could take it.)

- El ruido se oía de casa a casa.
The noise could be heard from one house to another.

- Ofrecemos servicios de puerto a puerto.
We offer services from port to port. (Let's suppose transport from one port to another.)


Side note: in Mexican Spanish, "clase" is the lesson taken, and you'll be understood that you have to take one class here and another there, because of the context; however, when talking about the classroom, we say "salón" instead. So, we'd say: "Ahora que voy a la secundaria (heard more often in daily speech), tengo que ir de salón en salón". ;)

de puerta a puerta ---> from one door to another (the kind of service DHL offers)

de puerta en puerta ---> one door after another (by knocking on doors all morning, like the Evangelical folk)

change puerta for whatever you need to mean locations. If you say "de pared a pared" (wall to wall), it describes a scope, or a span, or an expanse, or an extension: alfombra de pared a pared (wall to wall carpet) -never ever use en in these cases- atiborrado de piso a techo; corroído de proa a popa; sucio de la cabeza a los pies (or de pies a cabeza), etc.

Gracias, aleCcowaN. Tus explicaciones siempre ayudan a aclarar mis dudas.

Gracias, AngelicaDeAlquezar. Ya que vivo en la región suroeste de los Estados Unidos, tus ejemplos y regionalismos mexicanos son tan valiosos.