Bathroom odor

We live in a mobile home with 2 bathrooms. We smell a terible odor coming from 1 bathroom. Maybe the sewer gas Gail spoke of. It seems to be worse when its windy. Sometimes I don't notice it at all. I think I smell it worse under the sink.

Sounds like you have clog in a vent pipe on the roof (leaves, debris, ice and snow, etc.?).
When waste water flows through a drain/waste/vent system and the vent pipe is clogged, the system will create a "vent" by siphoning the water out of the nearest trap, allowing sewer gas back in through it.
Go up on the roof and clean out whatever is clogging it by hand if you can.
If it has gotten down into the vent pipe where you can't reach it, you may have to snake the vent pipe from top to bottom, and then flush it down with a water hose sprayer.
Good Luck!
Mike