I know that for the Chevy Roadtrek 190P rear forward facing seatbelts were an option and you could purchase a kit from a Roadtrek dealer to add it later. It included a seat cushion. I know because I got a quote for it for the 2004 I once owned.
That Chevy model had a metal bar right across the rear.
Liability issues are often mentioned when discussing adding belts. It's a real issue, passenger safety is a must. The kit for the Chevy's was likely the best option if not the only option assuming RT had tested it. I don't know if it was an option for the Dodge models.