A trailer wall segment (1A; 1B), comprising: a coupling element protruding from said wall segment at a first edge of the trailer wall segment; a receiving member arranged on a second edge of the trailer wall segment opposite to the first edge; the trailer wall segment being configured such that a trailer wall can be formed by connecting a plurality of said wall segments together, wherein, in said trailer wall: a first side of a first trailer wall segment is fixedly connected by means of welding, to a first side of an adjacent second trailer wall segment; the coupling element of the first trailer wall segment is received in the receiving member of the second trailer wall segment, the coupling element and receiving member providing a further fixation of the first trailer wall segment relative to the second trailer wall segment after the first sides of the first and second trailer wall segments are fixedly connected together; and the first and second trailer wall segments defining a passage between them on a second side of the first and second trailer wall segments opposite to said first side; wherein the trailer wall segment is configured such that, in said trailer wall, the coupling element of the first trailer wall segment and the receiving member of the second trailer wall segment at least partially define an air chamber into which said passage ends; wherein the air chamber initially widens when entering the air chamber from said passage to allow a primer and/or paint, to be sprayed onto the trailer wall built using the plurality of walls segments, to substantially fully penetrate the passage. a coupling element protruding from said wall segment at a first edge of the trailer wall segment; a receiving member arranged on a second edge of the trailer wall segment opposite to the first edge; the trailer wall segment being configured such that a trailer wall can be formed by connecting a plurality of said wall segments together, wherein, in said trailer wall: a first side of a first trailer wall segment is fixedly connected by means of welding, to a first side of an adjacent second trailer wall segment; the coupling element of the first trailer wall segment is received in the receiving member of the second trailer wall segment, the coupling element and receiving member providing a further fixation of the first trailer wall segment relative to the second trailer wall segment after the first sides of the first and second trailer wall segments are fixedly connected together; and the first and second trailer wall segments defining a passage between them on a second side of the first and second trailer wall segments opposite to said first side; a first side of a first trailer wall segment is fixedly connected by means of welding, to a first side of an adjacent second trailer wall segment; the coupling element of the first trailer wall segment is received in the receiving member of the second trailer wall segment, the coupling element and receiving member providing a further fixation of the first trailer wall segment relative to the second trailer wall segment after the first sides of the first and second trailer wall segments are fixedly connected together; and the first and second trailer wall segments defining a passage between them on a second side of the first and second trailer wall segments opposite to said first side; wherein the trailer wall segment is configured such that, in said trailer wall, the coupling element of the first trailer wall segment and the receiving member of the second trailer wall segment at least partially define an air chamber into which said passage ends; wherein the air chamber initially widens when entering the air chamber from said passage to allow a primer and/or paint, to be sprayed onto the trailer wall built using the plurality of walls segments, to substantially fully penetrate the passage.