Gentle tapping on the outside might come up with something as well...
I have added a couple of shelf projects over the years from the outside using the molly bolt or spring wings idea. worked good... In this case you want to miss the studs haha... I like the MOLLY BOLT over the SPRING WINGS as when you remove the screw from the spring wing it all drops behind the wall...
The thing that worked for me was to be able to mount the back board in its four corners then attach all your thing to the backboard. The backboard could be metal as well verses the wood you would use on the inside...
The angles pieces and adapter plates etc you find currently used usually are just screwed into the trailer outside wall using plane ole self tapping metal screws and alot of sealent.. I have done this for additional CABLE TV type connection boxes or PVC Electrical junction type boxes where I was gaining access to the interior through the center of them with larger holes...
I don't know about THOR but I do know you can contact JAYCO and provide them the VIN NUMBER of their trailer you own and they will immediately email you a PDF file with the information you requested. These are from their build packages...
Roy Ken