All I can say, Nick, is that the construction of the back wall (and the other two as well) consists of a thin, outer skin of painted aluminium sheet, with a thick, 3 or 4cm thick core of expanded rigid polystyrene foam, a sheet of expanded steel mesh, with a plasticboard inner wall. I believe that there are wooden battens inserted in the rear wall for just the reason you illustrate. If you cannot locate them (with an electronic “locator”) may I suggest contacting either your local Hymer dealer, who can get the answer direct from Germany, or one of the Parts guys (details on Spares page) who may be able to send you a diagram from their parts fiches, or finally, contact Hymer direct yourself (address on Home page) remembering to include your Exsis build number (on the silver sticker by the habitation door).
Please let us know what you discover .
Meanwhile there may be someone on here who has practical experience of this – I regret that I don’t.
Good luck!
Barry
