Dual batteries...
Having in mind the Flippac, a fridge, etc., I wanted to run dual batteries. My approach is similar to what many have done here, with one little twist...
First, I replaced the larger stock battery with two group 35 Sears Diehard Platinums. I decided to fab my own mount made from bent scrap sheet steel and riveted together aluminum angle. Both batteries are located in the normal stock battery location:
I also created an accessory fuse mount from a piece of Lexan for two 80A Blue Sea circuit breakers (one for an in-cab accessory fuse block and one that feeds the house fuse block in the bed), one Blue Sea fuse block, and a 500A solenoid (located underneath the mount in the above picture). The house fuse block is located in the passenger-side bed cubby, which feeds all the accessory loads within the Flippac.

To connect the batteries I used info from the "$50 isolated dual battery" thread (thanks FLHummer): so a 500A solenoid is tied into a switched 12V fuse such that the two batteries are connected when the car starts. Here is where the twist I added comes in... I didn't want the batteries to connect until the engine was actually running. There are a lot of ways to accomplish this, but I chose to add a relay tied into the oil pressure sensor. From memory this is my rough schematic:

The tricky part of this on the 2nd gen Tacoma is that the oil pressure switch acts on the negative side of the electrical system. So, when there is no oil pressure the switch connects to ground (chassis). When there is oil pressure the switch floats ground. This is why I had to add the additional relay, so that when ground is floating the relay closes/connects the load to the solenoid. Due to using a switched 12V source, the relay will only activate the solenoid if two things are true: 1) the ignition is switched on, and 2) the oil pump is producing oil pressure. Hopefully I explained that well enough.
This setup has been working perfectly for about 15 months now. It was cheap to make, but I recognize there are also more components involved that could fail than would be the case if I had purchased an off-the-shelf smart isolator.