OK I've finally got the rear batteries installed. I had to rebuilt this rack a second time or I would have posted this during the front battery install post. I also seem to have lost the picture of the rack by itself so you can really see the mounting points but there are four feet that come off from the sides and I used 5/16" grade 8 bolts to secure it to the trunk. Be careful that the holes are far enough out. I noticed that there are two layers to the metal work here and if you drill just past the sides of the trunk where it dips down you'll enter a cavity that you can't actually get to from the bottom and therefore can't attach the nuts to the bolts. You could use a lag bolt but that has a good chance of just ripped out with the thin metal here. Speaking of, use a nice wide washer on both sides to get a lot of surface area.
Here is the first picture that wasn't lost after the batteries are mounted.
Here is a top down view to show the room left over. Ah some storage space you say still....I wish. I've decided to, at least for now, use the jumbo charger inside the car. I'll probably replace it someday with something smaller and gain some room back....we'll see. If you look at the bottom of the picture you'll see some large metal feet that I've added. The charger will bolt to these.
Here is the charger in place with the BMS wiring all attached. This is kind of a fast forward in time shot really since if you look closely you'll notice I'm already charging as well. You can also see some unprotected yellow and red wires in the left side of the picture. These are the two sets of power wires for the charger (110v, and 220v). I haven't finished installing the final plugs for these so that still needs to be done.