I am sure this topic has been discussed before.
The fact that you may use vaults as a wall for the front of your cave like castle it is just dumb. We have a player with 8 vaults stacked in a mess of T3 foundations and else. It looks terrible and gross, and it should not be the way to defend your base.
I am okay that they are hard to destroy, and should be an strategic element within the game to spot where the enemy vault’s are. Also vaults should offer the possibility to pick them up within 15 minutes of placement to adjust location, fitting and such, and NOT BEING ABLE to be destroyed afterwards. Even when cost to produce is cheap, it will add an inch of pressure before you place it, so you would think twice before placing them (well defended spot, etc).
Apologies if any grammar mistake, english is not my main language.
Looking forward to your feedback.