This is my third iteration of storage boxes in my 16 so far. I am paranoid about stuff flying in the case of an accident. Will try and post some pics later this weekend.
I have some weight rated straps hooked between the back two tie down points. I bought 4 FrontRunner Wolf Pack boxes, added rated tie downs oops as handles through the side holes of the boxes, and used rated tie down loops/carabiners to attach them to the strap across the back. They are up against the back seats stacked 2 high. I also just ordered a Safari Straps, heavy duty, cargo net which will be hooked to all 4 tie down points and cover everything.
Each of the wolf pack boxes is modular so I can remove them when needed.
1) Recovery gear
2) Tools and roadside emergency
3) Emergency / survival / food / water
4) Air compressor, tire stuff, misc
If I go camping, I can removed the survival/food/water etc because I would have all that stuff in my camping gear. If I just need space to haul something I can remove all or a couple boxes easily. Prior to this I had 2 different single, very large, boxes that were too big and cumbersome to move easily.