J-Ride is several components. Some are easy to add, others difficult, some impossible.
1. Rear Sway Bar and/or Helper Springs, easily added at a cost of a few hundred
2. Bilstein Shocks, same as above
3. Computer balanced Drive Shaft. Can be done for a couple hundred or less, a rarely needed effort
4. Rubber isolators between Chassis and Body. Can't be added in practicality. I don't know how much they help. Our Jayco was built with them long before J-Ride was offered.
Items 1. and 2. can make significant improvements in a coach's ride, handling, and tracking. A heavy duty sway bar will actually stabilize a Class C on the campsite.