I like to use strut to fasten to thin siding. Even if you can't get at a structural member, you have more screws for support - as many as you like, I guess. If the conduit is on deep strut and the box on shallow strut, the conduit lines up with the threaded hole in a box better than I can bend an offset.
I don't really like the look of strut, but it does look nicer than conduit falling out of the straps.
