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.
Every day's a learning experience, though sometimes not what we expected.
2012 Jay Flight 19RD
2016 Ford F150 XLT 2X4 SC 3.5L Eco Max Tow
2010 Tundra TRD DBL Cab (Traded)
1 Spoiled Dog