Can you tell us where are those unbreakable chests or just high level crates? The only one with 11k hp that I found was at the spawn ship
The ones I grabbed were from the arena match for "The One" in Fort Joy. Also, I believe the chest where the heads tell you to open/not open it on the starting island may be invincible too.
Also, as for heavy crates with high health, look for the reinforced, metal, and heavy metal crates around the prison. There's also one or two on the boat I believe.
Before you get an invincible chest, you can mitigate the damage to the crate a bit by restricting the max weight inside of it for what will kill an enemy. Meaning, if you know 300 weight is enough to kill the starting enemies, then you can limit it to that weight until you need to put more in to deal with higher health pools.