It's not that simple, though there is a quick walkaround by using Navmeshes: just search for "navmesh" in the prop browser, select it and place it on the surface the characters are intended to move on. It won't appear in the camera view.
Creating a natively navigable prop (that is, a prop that can be walked on by the puppets) is far more involved, as it requires defining a complex template with two parts, the first of them a navmesh. Too bad, this is far beyond the capabilities of the Sketchup importer.
ars longa vita brevis - Hippocrates (attributed)
If you want to tell jokes then use Muvizu; if you want to make 'Movies', use iClone; but if you want to tell stories, use Moviestorm - PrimaveraNZ
Shared addons & stuff for Moviestorm: https://drive.google...aTNsSFBuN0sxZHM