Yep, those guys as WRV must have stayed up nights trying to figure out how to hide things from future owners and RV techs! The large pipe from the water tank (I know not its purpose) is sealed tight on the underside (not visible in the photos). I think the critter got into the bin by going over the top of the carpeted panel as there is a small gap between the panel and the coach floor. There are many potential sources of ingress into the main storage bins for small creatures. If you have one of these hidden panels in your coach you may want to remove the panel just to see what might be hiding out in there! And, yes, ain't it GREAT that we have this forum to share info that we glean about our coaches with our fellow Alpine owners. It is an invaluable resource!
Roger & Diana
'03 Alpine 36MDDS