As a first rule, you never edit the Native module or the Common Resource files. You already made a copy of the Native module, a good start, but everything which you create anew, even if it is a simple duplicate, should go into your module's texture and resource folder.
Make sure that
- the brf file is getting loaded in module.ini via load_mod_resource,
- the material and texture entries are in the same brf file as the mesh (they can be inside different brf files but then you need to respect the loading order; for beginners it's easier to just put them all into the same brf file) and are referencing the new file properly,
- the texture has been added into your texture folder
OpenBRF has a search error function with which you can check, which misstake might have happened at your new added meshes. There are probably still a lot of Native errors but you can just load more errors and scroll until you see the lines for your new added items.
I can't really help you with adding the item to the files via Morgh's Editor since I am using the Module System and don't know the need-to-look-for's of Morgh's Editor. You might alternatively also start getting used to the Module System. It's not as difficult as it looks like and in the longrun, depending on what you want to achieve, you can do more stuff at your module.
