A panel assembly for a railcar body comprising: a first panel and a second panel extending longitudinally along the body and adjacently to each other, said first and said second panels (18a, 18b) each having an inner wall and an outer wall with interconnections in between, said inner wall of each one of said first and said second panel having a longitudinal edge along which said first and said second panels (18a, 18b) are juxtaposed, said first and second panels (18a, 18b) having a welded joint created along said edges, said first panel having: a first mating interface extending longitudinally along said edge of said inner wall of said first panel and projecting transversely beyond said inner wall of said first panel towards said second panel, said first mating interface having a projecting portion having a chamfer at a distal mating end, said first mating interface being located on an inner side of said inner wall opposed said outer wall; and said second panel having: a second mating interface extending longitudinally along said inner wall of said second panel and proximate said edge of said second panel, said second mating interface having a guiding portion projecting at an angle from an inner surface of said inner wall opposed said outer wall of said second panel and creating a receiving open cavity there in between, wherein said guiding portion is operative to engage said chamfer and to guide said projecting portion laterally and vertically so as to abut against a wall of said cavity of said second panel so that said juxtaposed edges of said first and of said second panels (18a, 18b) are located at a predetermined distance from one another, characterized in that said inner wall of each one of said first and said second panel is longer than said outer wall of the respective panel (18a, 18b) and said first mating interface further comprises a recess projecting from an inner surface of said inner wall and below said juxtaposed edge of said first panel, said recess being located directly at an end of a gap between said juxtaposed edges, said gap opening on said recess. a first panel and a second panel extending longitudinally along the body and adjacently to each other, said first and said second panels (18a, 18b) each having an inner wall and an outer wall with interconnections in between, said inner wall of each one of said first and said second panel having a longitudinal edge along which said first and said second panels (18a, 18b) are juxtaposed, said first and second panels (18a, 18b) having a welded joint created along said edges, said first panel having: a first mating interface extending longitudinally along said edge of said inner wall of said first panel and projecting transversely beyond said inner wall of said first panel towards said second panel, said first mating interface having a projecting portion having a chamfer at a distal mating end, said first mating interface being located on an inner side of said inner wall opposed said outer wall; and said second panel having: a second mating interface extending longitudinally along said inner wall of said second panel and proximate said edge of said second panel, said second mating interface having a guiding portion projecting at an angle from an inner surface of said inner wall opposed said outer wall of said second panel and creating a receiving open cavity there in between, wherein said guiding portion is operative to engage said chamfer and to guide said projecting portion laterally and vertically so as to abut against a wall of said cavity of said second panel so that said juxtaposed edges of said first and of said second panels (18a, 18b) are located at a predetermined distance from one another, characterized in that said inner wall of each one of said first and said second panel is longer than said outer wall of the respective panel (18a, 18b) and said first mating interface further comprises a recess projecting from an inner surface of said inner wall and below said juxtaposed edge of said first panel, said recess being located directly at an end of a gap between said juxtaposed edges, said gap opening on said recess.