"I even thought about some sort of alarm system that could turn off all of the juice if a wire or set/string of wires got too hot."
Use fuses! The alarm to let you know there is a problem will be the power goes off! 
But everything is nice and safe!!
I aggree, freezers or refrigerators are ready made battery boxes. Get an old non-working one free. Lay it on it's back, doors up, sit batteries in, close doors.
I'll be using an old chest freezer in the back of a Box Van for alot of batteries myself. I will put a vent pipe to the outside of the truck to get rid of any gasses. Drill a couple holes for wires and install gromets or plastic pipe to protect my wires from cuts. I may bolt it to the floor, I may not.
In this case I am planing to charge batteries while I drive and use a larger inverter while camping. When the truck is sitting at home I will connect the battery bank to my other banks also to encrease the storage at home and to keep them charged.
I was actually trying to decide how to build a box and mounts for them so they would be safe while driving, then I realized an old freezer will work just as well for mobile use as stationairy and I need all the same things. Keep batts. cool in summer, warm in winter, prevent damage, protect the wiring, etc...
And once compresser and other un-needed items are removed an old freezer should not be all that heavy compared to a heavy wood or metal box to do the same thing.
