Welcome to airforums!
Mine is well hidden, yours may be in the same place:
Open the curb-side closet next to the bathroom (if you are in the trailer facing the front, that's the right side).
Get on your knees, and look at the bottom right side of the closet.
If there's a little blue door, you just found it!
This assumes you have a rear bath unit...
If it's to be, it's up to me.