After looking over the various options available, I installed an IBS dual battery system in my 5th generation 4Runner. I have the gauge in my glovebox so that it is out of the way but viewable when I want to look at it. I'm impressed thus far with it. I use an Optima yellow top as the 2nd battery. An ARB fridge is wired directly to it with an ARB wiring loom, and it seems to keep things cold consistently.
Greg (a.k.a. Hafwit)
1967 Steyr-Puch Swiss military Haflinger
1975 Volvo Swedish military TGB111
2011 Toyota 4Runner Trail Edition