Sorry for the late response.
I put a set of trojans in my passthrough and I have a set outside.
2 issues with this to note.
1. Gas venting you must SEAL your battery box.
2. wire length between batteries causes a temporary draw imbalance. Not a big deal if you aren't running the microwave.
MichaelO:
I drilled through the roof. Do not use your controller as a battery monitor. The tech at renogy told my it isn't accurate at all. I've also experienced this. In reality the blue tooth module doesn't tell me anything... I use a renogy battery monitor. You need a shunted battery monitor, anything else just guesses based on voltage which varies depending on battery/brand