You have to create a new root template and choose it from the Level Name drop down menu. Then you can add it to the level the same way as other objects. You see a yellow box outline of the level terrain and can place it somewhere in your level.
Thanks Windemere this was the part I was missing, I couldn't figure out how to include the level template in the global level.
What do you think would be the best way for Celludriel to distribute this though as obviously people will have to add this into the editor as a project in order to access his levels / level templates? This really doesn't fit a mod or addon since it targets the editor... (can a project even be uploaded to Steam Workshop? I suppose it could be zipped up and put on Nexus or the like...)
I was hoping Git could do it, but I'll have to investigate it further. It's also a huge workaround, we are basicly misusing the template system as a prefab system but if this is all we got, this is all we got. I'm glad it's figured out. Now if this works we should be able to build a big library project full of buildings for fast creating towns, outposts and other stuff.
My goal for now is give the tools to GM's to build the sunless citadel adventure in less then a weeks time. Although considering there are no twig blight creatures nor kobolds , there will have to be some artistic ... creativity. Maybe it's an adventure taking place after the sunless citadel conclusion ... I dunno ...