I can tell you what is wrong, and that you will need to use Maya or some other 3d software to fix it, but I can’t give you specific instructions because I don’t use Maya. At least you will know the problem and the terminology to find your answer.
The transparency problem is because the normals on many of the faces are reversed. The normal is the vector that the renderer uses to tell what direction a surface is facing. OpenGL which element and many game engines use usually renders only one side of a polygon. If the polygon is facing the wrong way, it is transparent. This is a common problem with a lot of free 3d models because a lot of modeling software display both surfaces of a polygon, and the modeler doesn’t know he needs to flip some of the faces.
There is an option in an element material to display both faces of the polygon, but I would recommend against it. If the normals are wrong, then your lighting will hit the surface wrong even if you display the back face. The best thing to do is to use your copy of Maya (or other 3d software) to flip the normals. This can sometimes be quite time consuming depending on the model, because often this isn’t a global change. Usually there is a mix of correct normals and reverse, and you only want to flip the reversed normals. This can sometimes mean a laborious selection of individual polygons, but for this model it doesn’t look like it should be so bad.
I would google flipping normals in Maya.
The texturing problem is because the model hasn’t been UV mapped (texture mapped). If all you want to do is apply a tiling Element grunge metal texture to it, a simple cubic UV map should work fine for this model.
Again google cubic UV mapping in Maya.
Good luck!
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