How many backpacks in the game?

[Itadaki]

In one playthrough how many backpacks are there in the game to enlarge your inventory? and where can they be found? thanks! yes I can google it but I just hit my data cap qq and only steam loads fast enough.

[Stoibs]

Off the top of my head:

1. Old house Save room
2. 2F Main House Master Bedroom Side Closet
3*. 1F storeroom of the ship, need corrosive acid to open. (Mia only, doesn't carry over to Ethan)
4. Radio Shack/Dock before the elevator to the salt mines.

[Itadaki]

Thanks! also is this for all difficulty or which one? item placement is random varying differences between difficulties.

[Stoibs]

Backpacks should be the same across all difficulties.