how to purchase outfits into cargo instead of outfit space?

[Goose]

^ title.

[Amazinite]

Deselect all your ships in the outfitter. Ctrl+click on your currently selected ship to deselect it. With no ship selected, any purchased outfits will go into cargo.
You can also hit u or r on a currently installed outfit to move it into planetary storage.

[tsingi]

I just click on [_] show outfits in cargo, which deselects all ships.
You can toggle [_] show outfits for sale. Leave it on to buy stuff to cargo.
I've been playing the Steam version on Windows 'cause my Linux box is sick, so it might be different.