We tow a 2013 CRV with our 2007 2350. We experienced the same thing as you, when not towing the RV handled fine. When the CR-V was connected it negatively impacted the handling of the RV, especially when passed by large vehicles pushing a lot of air. This started me down the path of doing several suspension improvements:
- Safe-T-Plus steering damper
- Rear sway bar (Roadmaster)
- Rear Trac-bar
- Front Sway Bar (Hellwig)
- Quiet hitch (eliminates any side to side play in the tow bar/receiver connection)
All this has helped quite a lot and I am pleased with the improvements. I don't get concerned with upcoming trucks anymore. I don't know for a fact, but I would bet the rear trac-bar made the biggest improvement for the passing truck issue.
I am not sure I am following your statement, "I don't think safe to stearate is the answer as it is probably the car that is pulling the coach." Also I am curious about what chassis you have with your 2350 (E350 or E450). I thought the more recent suspension improvements did not require all the upgrades that I made with my older 2007 E350.
JJ