What's your FG_SCENERY set to (if you use FGRun, it's on the page previous from aircraft selection)? You should move the Terrain/, Objects/ and Models/ directories from the RJGG download to that directory. As of 2.4.0, the shared models (altough Horacio's models are "static" ones, he decided to place them in the Models/ directory for some reason...) are loaded from FG_SCENERY, rather than FG_ROOT/Models.
You do see the runway/taxiways, do you?