LiPo batteries are so cool that they can also explode. I will describe my solution to avoid that. You have first to know that a LiPo battery is dangerous when it's use or charging, the storage is the safest moment if it's properly done. By the way, this post is also applicable to the Samsung Note 7. ;)
I used a metal toolbox with levels. I bought it new around 15.00€. I added multiples layers of strong aluminum foil on the bottom and sides.
We're never safe at 100%, so I added a LiPo SafeBag (Ideally, we would put one per battery but that would be expensive).
You can also buy a fire extinguisher with powder (not water). I bought a small one of 1Kg ABC.
You could drill the levels and add water bags, then if there is fire, the bags would melt and the water go directly down to the battery in fire.