Abstract: Internally insulated or packed panels house a thermal structure such as a heat recovery steam generator (HRSG). In a first embodiment, each packed panel has a cold pressure casing with an insulating layer covered by a liner plate. Welded collar studs are fixed to the cold pressure casing to secure the liner plate over the insulating layer. Small, movable end covers are provided at the edges of each packed panel to provide an adjustable panel joint. End covers of adjacent panels are in compression contact when an externally applied weld is provided between the cold pressure casings of adjacent packed panels. Each end cover is movable about each packed panel by means of oversized or slotted holes in the liner plate and end covers that receive each collar stud. Benefits are faster field assembly and allowance for thermal growth while preventing gaps and their associated hot spots from forming at the panel joints. A second embodiment employs a larger end cover in place of a smaller end cover and liner plate.