"SCS Box Trailer" includes all of the trailers listed as "STD" in-game.

Dry Freighter, Insulated and Refrigerated trailers use mostly the same templates, they're all named "Dry Freighter" in these files.

"Long" refers to 2- 3- and 4-axle trailers.
"B-Double" refers to the short trailers used in the B-Double chain type, and single trailers with 1 axle.
"Double" refers to the short trailers used in the Double chain type only.

Side Door and Moving Floor templates are only slightly different, they're all available in the "Individual parts" folder of the PSD file.