Most put it over the right rear tire. And I've never had a problem with batery fumes with mine. But a good idea would be to get an optima battery because of their dry cell. So you'll never have battery acid in the trunk or in your battery box. I don't have one yet but it's on my wish list.
I have mine located in the back pass side corner. I had my tank dropped to install a new fuel pump at the time so I didnt have to worry about putting any holes in it. I couldnt smell any fumes either