Yeah, each query is unique so there's no guarantee this method will work in your case. But it's worth trying USE INDEX/FORCE INDEX with various syntaxes. You could try using INNER JOIN - then you could get rid of the WHERE clause - who knows, maybe the optimizer is misled by the WHERE?
Alternatively, you could fetch the ids of last 4 trailers in a separate query, the index should be guaranteed (I hope...!) to be used:
ORDER BY trailer_id DESC
If this is successful you can use IN() clause in the second query without the LIMIT. How optimal that is - I don't know