This mod adds a flat zone around the Orcus Patera base so it can be used in Orbiter 2016. Install the original base from here first:
http://francophone.dansteph.com/?page=addon&id=162
Then extract this archive in orbiter root.
You can also install this base using the Orcus Patera 2016 orb recipe on orbiter-mods.com
Have fun.