A device for attaching to a surface of a wind turbine blade is described. The device comprises a plurality of sections to be arranged end-to-end along a portion of the blade. Each section of the device comprises: a baseplate for bonding to the surface of the blade; a first panel extending from the baseplate; first and second end walls extending respectively along transverse edges of the baseplate and the first panel; a first tab extending from the first end wall; and a second tab extending from the second end wall, the second tab being transversely offset from the first tab. The tabs are arranged such that when the sections are positioned end-to-end with a first end wall of a first section adjacent to a second end wall of a second section, the first tab of the first section overlaps the second end wall of the second section, whilst the second tab of the second section overlaps the first end wall of the first section. An associated method of mounting the device is also described, which avoids the risk of compromising adhesive and/or sealant during the mounting process.