You might consider those air foil, air spoilers for the back of your RV to help stabilize it in both winds and from passing semi's. I put them on last spring and really think they help. A lot. I always keep my 22.5 tire pressures up over 100 PSI to reduce wear and noticed a slightly higher incidence of road wander during winds. After installation of the spoilers noticed that wander was reduced. I wrote a product eval and posted it to my blog if you're interested. Articles content and conclusions are entirely my own...
V-Spoilers Product Evaluation