I run a dual battery set-up on my '08 TRV.
I DON'T use a battery isolator, but run the battery(s) in PARALLEL. I tied the 2 together by running POS -POS and NEG on battery 2 to the frame. When hooked together this way it's basically a BIGGER capacity battery. My choice was a WALMART tractor battery. ($25) I've doubled my overall battery capacity and haven't had any issues with my stator.
The install required very little modifications and I set the battery on about 2" of foam inside the battery box to soak up vibration & shock. All my battery connections are coated in anti-corrosion and the box inlets are sealed with silicone.
I've found that every spring I have to inspect all my connections, and clean/tighten as needed.
I run ALOT of accessories in the winter when plowing and having 2 batteries has proven to be a good "mod"
I'll also throw in that the TRV uses a 1.5amp battery maintainer 24/7/365 when not in use.