Billy, something like the Kettleman air ride system may help. I've never dealt with softening the ride of a truck while towing a fifth wheel. I have no experience to offer.
What I will say....with a longer motor home, in the 34' minimum range, your wife can get up and move around. An hour in the passenger seat, get up, move around, stretch, and then maybe an hour on the sofa or even in a recliner. Last weekend, we transported two of the grandkids home from a trip. My wife sat in the main cabin with them. In our coach, the recliner can be partially extended while underway.
The Class A passenger seats are usually more pillow like and recline. I have a terrible back and find that I'm most comfortable in my motor home seat.