I just pulled the jack/tool cover behind the rear seat. Seems there is approx 6 1/2 x 10 x vehicle width (didn't measure because didn't think it would matter as you could 3-4 batteries wide). So how about a sealed battery or multiple even in that location? With a little work I think it could even remain hidden and flat with the rest of the seats when folded, and stock tool storage shouldn't be an issue.