Someone with more experience than I have will surely have your answer, however, I can give you a couple of places to start. First, I assume you are talking the entire window opening as it would be used for an emergency exit. If that is the case, there is a good possiblity that the gasket is gone. That will keep it from sealing properly which could allow for the jarring loose. If that is okay, make sure that the screws that hold the levers in place are tight.
Next thing is to call Casita
at 1-800-442-9986. Talk to Jay or Susan. They will help you decide what is wrong and help you get it fixed. Their parts are priced better than you can get anywhere....and you may not even need a part. Regardless, they don't care if you have a new one or old one (mine's and '89), they are very helpful.
Park closures: I thought that the Corps of Engineers has closed two of their parks because they weren't accepting reservations on the web. What I found out is that the Corps turned them over to the cities they were in. So always double check. If the one you're are refering to is in the Texas Hill Country, then it may have been involved in one of the floods this year. But you probably already know that. I really believe you will Enjoy the Hill Country. It has got some great places to see!