I think the deadbolt is a good idea. I would caution you about using a flip knob on the inside though as anyone could reach through the window and flip it open while you're inside sleeping.
Here's another reason why I want a more secure lock. On my recent trip to Yellowstone my microwave
fell off of the shelf (the strap broke that was holding it down) and it hit the door. The tiny latch must have opened and when I got to the campground I noticed the microwave
was gone and the door was slightly ajar. I felt terrible as this could have caused a SERIOUS accident to a motorcyclist or a driver behind me.
I know another poster wonders why I want a lock and compares it to tent camping. I can tell you that last summer someone opened a sleeping camper's door and stole their wallets, Purse, and IPAD while they were asleep. Yes, they probably shouldn't have left them inside the camper but not EVERYONE in a campsite is honest or trustworthy. I know a lock won't stop someone who REALLY wants to get in but at least they cannot QUIETLY or EASILY get in to the camper if there is a good lock on the door.
I like the idea of a deadbolt, I'll look into this idea.
Thank you for the collaboration folks!