Installed new Optima Yellow Top in the ZHP. Removed the OEM battery (I believe it was the stock, original BMW battery), OEM battery tray, and installed the Optima using a Blue Torch Fab battery mount. BTF makes stuff for off-road vehicles, and the battery mount fit almost perfectly in the stock vert battery location. I am not 100% happy with how it is secured, but it isn't going anywhere so it will work for now.
I will touch up the white paint that got dinged up during the install (mount comes in bare form, I sprayed it with rattle can primer and paint). Plan is to take the top part of the mount and add some BMW blue squares to mimic the Bavarian flag, but I ran out of time to finish painting.