Alex, as you have glued the module down, guess it will stay (no air gap), not the best for cooling but they also can get pretty hot mounted to an iron roof (shed or house).
Think of maybe getting 4 gutter mount bracket (steel) similar to those used to mount/attach(bolt) to the ARB roof rack and modify them by under slinging a 2 lengths of aluminium hollow box section (say 40mm sq X 2.5mm), with spacers if req'd, going from the L-R hand side BRKTs (one both front and rear), passing over the top (each ends) of the aluminium panel frame extrusion and dropping down angle corner locating tabs that are attached to the aluminium rack hollow box section. This will prevent the panel from going Fwd, AFT, lifting and moving sideways. Use some rubber strip to protect frame/rack interface (no need to mechanically attach panel frame to rack box rail section).
Gosh mate, should have read your post a bit closer as U covered most of this.. b. glasses. All good.