My apologies for not having a better understanding of the context of the image you provided. OK, so which wall in the image is the outside wall? There were no stickers on any surface noting where the vent should go? If the 'back' wall in the image where the outlet is located is the outside wall, perhaps a stud finder can be useful. If the RV's exterior skin is fiberglass, you might even be able to infer the location of framing members from that side...
Sorry I have not been very helpful, and hope you find a more knowledgeable set of comments from another member here that has your model vehicle... Best of luck in getting the installation completed to your satisfaction.
2007 Tour Master T40C
Acura MDX toad
"It takes a great deal of time to recover from any improvement..."