That is a very good question.
I don't believe that it has a very good answer though.
Trip Planner - in Basecamp and on the XT - relies on a sequence of route points (Via Points, Shaping Points - any of which can be create first as Waypoints). This is called a Trip. Both the XT and Basecamp then calculate a way of getting from one route point to the next - always maintaining the correct sequence. This is called the route.
Explore doesn't behave in the same way. You can create Waypoints, and the Waypoints will synchronise automatically to the XT.
You can create a 'route', but the route consists of a series of drawn straight lines. When a route is synchronised to the XT you can select Where To->Explore->Routes and select the route that you created on the Explore site. Now, instead of it being straight lines, the XT calculates the roads to travel for itself, but it visits all of the places that you clicked on using the Explore map in order to change direction. Interestingly, the preview map shows the straight line version, the actual map shows the version with the roads calculated.
When navigating, this behaves exactly like a standard route - in that it gives turn by turn directions. But - it doesn't have any routing points to keep it in place. This means that if the route is forced to recalculate (say if you wander away from the plotted route), it will take you from wherever you are now to the end.
You may have transferred Waypoints - but they are not part of the route. These are just places that are shown on the map. The route may or may not pass within a cm of them - but they are not part of the route, holding it in place.
The XT can convert a course into a 'Trip' This is confusing. They have now used the word 'Trip' in a different context. When it is created, it is saved in the Trip Planner App on the XT. But load it up, and there are no intermediate route points. If you try to edit it, it loses the course that it has plotted and takes you the fastest/shortest way to the end. But you can navigate it and it gives you spoken directions. And here is the interesting part - which almost makes it quite useful (personal opinion) - it will not recalculate if you deviate from it. In that regard, it behaves like a Track. I tend to refer to it as a TripTrack so that I know I am not talking about a normal Trip of route points. But if you do deviate from the plotted course it then finds the closest point on the TripTrack that it has calculated, and plots a route to get you to that point.
You can see an example of this with screenshots in this section of a document that I published on here. This jumps in at P61, but the whole of that section 7 is to do with Explore and the XT.
app.php/ZXT-P61
To get what you wanted - you can create the waypoints on Explore, synch them with the XT, and then build a trip in trip planner using those waypoints. But Explore iteslef will not construct a route or a trip that uses Waypoints. Not yet, that I have seen anyway.
) and then sync Explore on the Zumo XT via Drive (whew!!!).