We splurged last year and had the box put on our 19. However, we really don't use it for storage. I noticed we were picking up a few rock / road debris chips in the fiberglass and the box seemed like it would an excellent solution for front end protection. I have to admit, it is a good place for the batteries but I'd be worried about altering tongue weight too much if the box accumulated much stuff. Don't want to mess with our "equilibrium".
We do regular purges to get rid of things that aren't getting used. It's real easy to throw stuff in because there's lots of space. The joke with us is, if it doesn't have at least 2 uses, it can't come. At the end of the day, it's camping and we like to keep it simple.