We really like our Springdale. It has everything we need and the quality seems to be holding up to our three kids. You can see pictures of it at my blog (link below). You all are going to have a blast.
I don't blame you for being concerned about the door. What ever it takes to get piece of mind. The red lock on our door seems to be along the lines of a dead bolt but smaller. If you need an alarm, maybe consider something like this one Wal-Mart Link
. It will just hang on the door and sense motion and such.
Speaking of safety. We have a similar layout with bunks (kids) on the other side of the RV from our bed. I keep a "fire blanket" near our bed. Just in case there is ever a fire and I need to cross the RV to help the kids get out the escape. Never thought of something like that until I heard it on a pod cast a few weeks ago.