[Carl n Susan]

This is not a new problem. You really need to secure the door as the plastic latch isn't adequate. As for a replacement, your Montana dealer can order one. It is a little pricey. Better idea is to read the following thread. On page 2, SlickWillie provides a link to a supplier and a little bit later Art n Marge provides the actual model number you want.

http://www.montanaowners.com/forums/showthread.php?t=38776&SearchTerms=sewer,door