The most common and most likely answer to this crossword clue is the 7 letter word PREVIEW
I've seen this crossword clue in The Guardian
P
R
E
V
I
E
W
More clues leading to the result PREVIEW
- Gun I stashed in seat in trailer
- Trailer parking right alongside edge of rifle range
- Trailer parking needs formal assessment
- Advance screening of power survey
- Sneak look at conductor ignoring new duo playing
- Quiet appraisal of trailer
- Seat about six inside trailer
- Papa about to struggle with Western, cinematic event?
- Vicar: ‘One must sit in seat in church and look ahead‘
- In advance, see vicar, one occupying bench
Buddy explains!

The straight part
We know that "trailer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trailer = preview.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PREVIEW mean?
PREVIEW noun- An experience of something in advance.
- An advance showing of a film, exhibition etc.
- Something seen in advance.
- A facility for seeing and checking a document, or changes to it, before saving and/or printing it.
- To show or watch something, or part of it, before it is complete.