Hi AS! Yes, for longer term storage, most of these recipes would likely need some type of preservative.
I haven’t experimented with this idea, so I’m not exactly sure which ones would benefit best and how much preservative you’d use.
But you’re right that Liquid Germall Plus would keep any high water content products fresh longer, just keep in mind that it’s not suitable for sprays that go airborne.
You might also want to explore sodium benzoate or potassium sorbate, or experiment with other natural preservatives that don’t have an aerosol restriction: :)
https://thenerdyfarmwife.com/natural-preservatives-for-skin-care/