I use to have my ARB 50L Fridge in the back on a slider on top of a platform I built, however we were always wanting access to food/drinks while on the road. This summer I removed the middle seat in the second row and placed it there....couldn't be happier and the fit is perfect (see below). Center seat was ideal to remove for three reasons (1) middle seat is the simplest to removed (no wires for heated seat or flip back mechanism for access to 3rd row) , (2) when in the center makes it very easy to access from the front seat, and (3) makes for an awesome armrest for the back seat passengers
. For dual battery controller I went with the traxide USI-160. Here is the link to the LR4 kits:
http://traxide.com.au/complete-diy-dual-battery/land-rover-dbs-kits/discovery-4-dbs-kits/
BTW - that is my LR3 and platform in the link you listed above.
ARB 50L in 2nd row with center seat removed -
View attachment 319780
On platform with slider