[RayChez1]

It might be something in the bottom compartments and the smell is just coming from the opening under the frig. I believe the furnace is right under the frig. I would check the bottom compartments for something that might have spoiled or maybe a mouse got into your coach and died.
Other problems could be a leak on your black tank connections.
I had a smell like that on my coach a couple of years back and I had a hard time finding out what it was, so I bought some commercial janitorial disinfecting stuff and sprayed all the compartments where the tanks are located. I also took my barbie grill out and washed real good, vacuumed all the compartments and sprayed the disinfecting stuff all over. Smell went away.