Black water tank
I wonder if the seal on your toilet valve or the seal at the floor has gone bad. Does the bowl hold water? Have you tried leaving some water in the bowl while youíre gone? That will leak down if the seal is bad. Then I wonder about the toilet base and how good that seal is. Also wondering if your sink trap/shower trap is holding water. Sometimes the gray tank can smell bad, too, and in some trailers, the bath sink is plumbed to the black tank. Make sure thereís a few cups of water poured down the drains, especially if you donít use them (sounds like you do, but just in case).