I got the following response from Roadtrek Service:
"The alarm system was not installed by Roadtrek and may have been installed by Dodge as part of the original unit.
This would be something that a Dodge dealer should be able to help you with maybe."
I am assuming from this that our van did have an alarm system as indicated by the previous owners. I confirmed this the hard way. I think if someone were to break a window, pull up a lock button and open the door the alarm would sound. A few days ago around 6AM at a nice quiet campground, with all the doors locked the previous evening via the key fob, I pulled up the lock button and opened the door. The horn honked about 4 times before I was able to get to the key fob and disarm the alarm. An embarrassing but learning experience.