Ours is like the above. As far as 2 not working....well, they may have been installed by the same guy that didn't know which direction the water flowed..
The backflow preventer is under our bathroom sink. If you have 2 it may be under that sink as well. I'm not familiar with your trailer but I have a friend that bought a new Big Horn and his backflow was backwards as well. They had to cut the wall out to get to it....
