Robert,
I am not sure exactly how your coach is laid out or which closet you are referring to, however there is usually a access panel or mirror or something to allow access to plumbing areas. In my closet where the vacuum breaker is located you can remove 6 or 8 screws and access the plumbing which is behind the drawers. The rest of my plumbing is accessed under the bathroom and kitchen sink, or by removing the wet bay cover. That access is tight.
If you find where it is leaking it may be easier to simply bypass the old line and install a new pex line wherever you can snake it through. If you have a ice maker than you can get to that area from behind the refrigerator or the drawer below it.
Hopefully this will help you some.