El camerino en que guardamos el mobiliario tiene insonorización.

Yes. En que introduces a relative clause meaning in which / where. After a place noun like camerino, Spanish often allows donde, so El camerino donde guardamos el mobiliario tiene insonorización is also correct and sounds very natural.

In general:

• en que = a bit more formal or written
• donde = very common in everyday Spanish
• en el que = also correct, a little more explicit

All three can work here.

The meaning is basically the same: the dressing room in which...

Spanish allows que after short prepositions such as en, de, con, and a when the noun being referred to is already stated:

• el camerino en que...
• el camerino en el que...

So why choose one over the other?

• en que sounds slightly leaner
• en el que sounds a bit heavier or more formal
• in everyday speech, many people would simply say donde

Because here que is a relative pronoun, not a question word.

• que = that / which / where in relative clauses
• qué = what in questions or exclamations

So:

• El camerino en que guardamos el mobiliario... = relative clause
• ¿Qué guardamos en el camerino? = question

That is why there is no accent mark on que in your sentence.

In Spain, camerino usually means a dressing room or changing room used by performers, presenters, actors, etc., especially backstage or in studios/theatres.

It is not connected to the English word camera. Depending on context, translations could include:

• dressing room
• changing room
• backstage room

Because the sentence states a general fact or habitual use.

Guardamos el mobiliario does not have to mean we are storing the furniture right now. It can mean:

• we keep/store the furniture there
• that is the room where we usually keep it

Spanish uses the present this way very often, just like English:

• This is the room where we keep the furniture.

Guardamos is the first person plural of guardar, so it means we store / we keep.

The ending -amos tells you the subject is we. Spanish often leaves subject pronouns unstated when the verb ending already makes the subject clear.

So:

• guardamos = we store
• nosotros guardamos = the same, but with the pronoun made explicit

Not in this sentence. Guardar often means:

• to keep
• to store
• to put away

So guardamos el mobiliario means we store / keep the furniture.

Although English guard and Spanish guardar look related, guardar is very often about keeping or storing, not only protecting.

Because mobiliario is usually a collective noun meaning furniture or furnishings. Like English furniture, it is normally used in the singular when talking about the set as a whole.

So:

• el mobiliario = the furniture / the furnishings

You would not normally say los mobiliarios for ordinary furniture in a room.

Yes, you could.

The difference is mainly nuance:

• el mobiliario = more collective, sometimes a little more formal or technical
• los muebles = more everyday, focusing more on the individual furniture items

So both are possible, but they do not sound exactly the same in tone.

Literally, it means has soundproofing or has sound insulation.

The noun insonorización refers to the feature or process of reducing/blocking sound transmission.

A very common alternative in Spanish is to use an adjective:

• tiene insonorización = it has soundproofing
• está insonorizado = it is soundproofed / soundproof

Both are natural, though the adjective version often sounds a bit more everyday.

After tener, Spanish often omits the article when referring to a general feature or facility.

Compare:

• tiene calefacción = it has heating
• tiene aire acondicionado = it has air conditioning
• tiene insonorización = it has soundproofing

If you add an article, the noun often becomes more specific:

• tiene una insonorización excelente = it has excellent soundproofing

So the version in your sentence is completely normal.

The accent mark shows where the stress falls: in-so-no-ri-za-CIÓN.

Without the accent mark, standard stress rules would make the word sound different. The written accent tells you that the stress is on the final syllable -ción.

This is very common with nouns ending in:

• -ción
• -sión

For example:

• información
• situación
• televisión
• insonorización

It breaks down like this:

• El camerino = the subject, the dressing room
• en que guardamos el mobiliario = a relative clause describing which dressing room
• tiene insonorización = the main statement, has soundproofing

So the sentence is built as:

[noun] + [relative clause] + [main verb phrase]

In English, the structure is very similar: The dressing room where we store the furniture has soundproofing.