Thanks for helping, Frogman.
It seems that, as usual, there are only certain circumstances where you will have this option.
The one that works every time is:
When you stop guidance (click the flag at the top-left sidebar), a dialog box follows with Stop (or Start) Guidance. When this box is highlighted, click Option and you will see Store Trip under the Map heading.
I saw the Store Trip option a couple of other times, but couldn't recreate it... once, while getting guidance with just the Nav Map on-screen, I clicked Option and it was there. This would seem logical -- storing a trip while being guided sounds like an intuitive thing to do, but I haven't been able to recreate this scenario
Frogman - to clarify the option you mentioned: "to store the single address you sent from Google, you can just click Option and select "store in vehicle
"... the option I see is for creating, adding or storing Contacts. That's useful, but there's no way to store them as trips directly from here.
So I guess the idea is, you get to your destination, stop the guidance and store the trip. If you want to store an address from Google as a trip, just start a fake trip and abort.