Smoove (the Sandbox tool) does not work in Sketchup Make 2017 (latest, 17.3.116) running on MacOS Mojave 10.14.3. I can create a terrain grid from scratch but I cannot edit it in any way. And as I understand it, there are no plans to ever update Sketchup Make.
None of the Sandbox tools work on Sketchup Free. (And the smart money is on that not happening soon, if ever.)
So the only way to model terrain now is to pay $300 every year for Pro?
Let me add my vote to those that think the move from desktop-based Make to web-based Free is a bad idea. Regardless of what all the ex-Google developers at Trimble try to tell you, the reality is that web-based apps like Sketchup will never be as good as if they were desktop based. Not even if bandwidth becomes free, infinite, and 100% reliable…none of which will ever happen.
I’m afraid that for me, Sketchup is now history. So sad to see a once great app destroyed.