Abstract: A panelled assembly has a spacer 26 of cuboid, or rectangular prism, shape located between adjacent first panels 16 in order to maintain separation of the panels 16 at a desired minimum distance during mounting of the panels. During installation, the spacer 26 abuts the first side edge 16b of one panel, and then the second side edge 16d of the circumferentially adjacent panel is made to abut the opposed side of the spacer. This results in an axially extending gap 28 of a constant width between adjacent first panels 16. Similarly, spacers 26 are located between adjacent second panels 18, adjacent third liner panels 20, adjacent fourth panels 22 and adjacent panels 24 as the panels are installed to make up the assembly. This results in axially extending gaps 28, each of a constant width, between circumferentially adjacent panels. The material from which the spacers are made is substantially the same as filler material which is used to fill the gaps between adjacent panels caused by the presence of the spacers.