There are only two set ups for shoulder belts; those anchored to the vehicle wall ( door frame) and those with the shoulder belt in the seat back; that I personally, have not seen in a Class A application.
Both are better than lap belts alone, but finding the seats with the belt in the seat back, that will safely attach in your coach could be a long and costly process.
Somewhere I have a link to a site that has , motor home seat belts, when I find it I'll re-post.
EDIT : Got back in time to add to this post.
OK , I can't get the link to work. Google , Wesco Performance, then RV seat belts, installation videos posted there.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.