Towing behind motorhomes can be a big problem because of all the turbulence coming off the flat back of the motorhome. We have so far broken two trailer tongues towing cats behind a motorhome. In both cases the trailers had long, straight tongues without triangulated stiffening arms, and I think this is an important factor.
The turbulence behind the motorhme would cause the trailer to oscillate back and forth and eventually break the tongue.
The scary thing about it is that the tongue breaks behind where the chains hold the trailer to the vehicle. So when the tongue breaks, the trailer is on its own.
That's why I am thinking that maybe those "Airtabs" would work on the back of a motorhome to decrease the turbulence for the trailer.
Turbulence may be only part of the problem. You should also look at weight distribution on the trailers. Try moving the center of gravity forward or backwards to see if the oscillations change in frequency or stop. You may also want to look at moving the axle on the trailer.
If you do decide to modify the air flow you may want to consider a solid mud flap type panel or even one of those broom things that extend across the back of the RV below the rear bumper. That should reduce or eliminate air coming up off the rear of the RV and lifting the trailer.
