Thx for feed back. After pricing similar add ons--decided to start with Coleman free standing 10 X 10 screen room. Will consider the Thule enclosure for future upgrade.
A free standing screen room can be left setup on your campsite. Then you're free to drive your van away for exploring and it keeps someone from taking your campsite.
That was my other thought. In addition, the 10 X 10 Coleman comes with a heavy duty bag that fits across the van in front of the back seat. It is out of the way.