a question in between:
where do you install the second battery? Under the passenger seat or under the VAN on the frame?

 

There is a factory option for a second auxiliary battery that mounts to the frame, somewhere just behind, just under the driver. The cheapest I have found the factory mount is $50 roughly, plus shipping. The other year I was thinking I was going to mount them inside and save the money, but I am glad I not going that route. I'll save valuable interior space and even with sealed batteries there are vents for hydrogen to escape. They should be mounted externally so they breathe freely.

https://www.tascaparts.com/oem-parts...iABEgKuifD_BwE

 

https://chevroletforum.com/forum/exp...97/#post362014

 

Hydrogen isn't an issue with one battery.You're right about the real estate though.