I just checked on the 2010 FC parts list to see if the 19' shower door is still the roll-away we have on our 2002 19' Safari Bambi. As far as I can determine, it is, so our experience may be relevant
It took several years before our shower door leaked and it was not apparent where the leak came from. We ended up recaulking under the lower rail of the door and that held for a year or so, then the leak reappeared. After much investigation with a flashlight and various probes, we determined that the caulk, even when it looks perfectly okay, cracks away from the shower enclosure and the lower rail of the door. Removal of the "loose" caulk and careful, thorough caulking of the gap between the lower rail of the door and the shower enclosure has, once again, stopped the leak.
The leaks probably develop due to the flexing of the trailer while driving. After a year or so, the caulk is no longer so flexible and it cracks away from the shower enclosure. The cracks are almost impossible to see. We now carry a tube of caulk with us!