I can't offer an automotive specific book that I thot was worth the purchase price. It may exist, but I've not seen it yet. I've not looked very hard either, so keep that in mind.
What I'll suggest is a book written for boats. They tend to deal with the sorts of mods made to Expe type vehicles. The auto books are written for guys building hot rods, which while still 12 VDC, isn't quite the same. They don't usually bother with stuff like dual batteries, etc. The books written for RV's that I've seen somehow left me wanting. Maybe it was a perception problem on my part, but their approach & methods seemed less robust than the marine stuff.
HTH