How do i replace cargo rack crate?

[DaringClarky 3]

So ive found that i can build another cargo rack and replace the crate if i have the spare cargo rack in my inventory.

 

However, i cant build just the crates on their own. Or can I?

 

It kinds defeats the point in having an empty crate if the resources to make a entire rack are the same as replacing the crates.

 

Is this the way its meant to be or am i missing something?

I have all engrams and everything unlocked.