My original suggestion of just removing the passenger side of the bunk base, covering the storage locker is just four screws that are easy to access. You do not want to drill a hole into the battery. A vacuum to catch the bits from drilling, or remove the right side battery before drilling anything is better yet. Then you will need a right angle drill to drill two two holes for, one for the cable now attached to the battery to go to the shunt, and one for the cable from the shunt back to the battery. Mounting the shunt next vertically would work, but you are going to need to extend the battery cable at #1 into the compartment next to the inverter to connect it to the load side of the shunt. I've also read elsewhere to be sure to be disconnected from shore power, turn the battery disconnect switch to off and cover the roof top solar panel. There is also the supply cable running from the B1 connection on the shunt to the most positive terminal which is the terminal on the left battery in the photo. That goes on the load side the shunt after connecting the short cable between the battery side of the shunt and the most negative terminal at Point #1. I'm interpreting that to be the black cable coming into the battery compartment from the left side that had been disconnected from the the photo's point #1. One thing I noticed in the Victron instructions was when reconnecting the cables do the battery's negative pole last.
![victron battery monitor install victron battery monitor install](https://2smoc9hdrhc9eko13nc-cdn.plushcontent.com/uploads/files/xh/3wkux4dr6yrjrlgy.jpg)
My problem is drilling a pilot hole in such tight spot. It is a tight fit but it seems to work if the shunt is mounted vertically on the side of the battery compartment closer to the inverter. ( MONITOR-VTBMV-S.pdf) I'm considering the option of mounting the shunt inside the battery compartment in the small space to the left of the batteries in the photo.
![victron battery monitor install victron battery monitor install](https://i.ytimg.com/vi/8yetV6zBO9E/maxresdefault.jpg)
AM Solar has a wiring diagram for installing the BMV 712 with two 6V batteries.