Thanks Matt,
I think that part of my confusion has been coming from equating "Layout Mode" to "Paper Space". I was also expecting to see the median ditch drawn, as evidence of a successful sub-assembly insertion. If it is "gonna look like that in Layout mode forever" I'm just going to have to get used to that concept... 🙂
As for it not working in my corridor, I am nowhere near ready yet to make that determination, as I have gotten only to this point in creating my assembly. I created the corridor selecting the assembly baseline, in the hopes that this might change something with regard to median ditch visibility, but it didn't.
I then became completel;y confused when I reverted to building the ditch using first LinkWidthAndSlope (that worked) and then LinkToMarkedPoint. The latter gave bme the exact same result as I got earlier with LinkSlopeBetweenPoints.
I will soldier on then and complete the assembly construction, assuming that this will work. Hopefully I am not still missing something here!
Peter