I don't have a MH, but you can definitely get an answer by going to your fire department, or police station, with your seat, and they'll be able to tell you where, and how to install it properly. They are trained in that aspect.
The MH I did own years ago, had seat belts for the couch.
2012 Jay Flight 19RD
2010 Tundra TRD DBL Cab
1 Spoiled Dog