Lots of answers here. Thanks everyone. The relocation kit includes an aluminum box, 15 feet of 1 gauge red wire, and 2 feet of black, connections, securing straps, etc. The box will be secured to the floor, fabricating a bracket to the rear seat belt mounting points. It's vented; although, I don't think that makes any difference using an Optima battery. They aren't "gel" batteries; but, "AGM", absorbent glass mat. They claim "virtually spill-proof".
FFIM is out. I researched that years ago and made the decision not to go in that direction. Not sure how much "extra stuff" will be required under the hood. The battery cut off should be reachable from the driver's seat, so it won't go up there....
I spent ten years in auto parts. Never once had issues with batteries in the stock room. Sure, they're dangerous, yes. I talked with a trash truck driver who told me that a battery in his truck, when the trash was compressed, would turn the truck into a bomb. I'm not sure I believe that... there are enough evil people in this world that you'd be hearing about it all the time. At any rate, I didn't dispose of my old battery that way.
Two fire extinguishers are on the shelf to be mounted close to the driver... away from the battery... and at the moment, I have little idea what I will do with the space other than prep it and paint it.
IJ., that sounds awful! I'm sorry to hear that it
"killed you", too. I hope the land down under is Australia, not a grave
Thanks again for all the ideas.