I ran two friction bars on a 31.5 ft TT and never had a second of sway. I now use one sway control on my Pop up camper.
No sway control using friction as the basis of sway resistance is designed to stop a badly set up trailer. Many will argue that dual cam sway control is premium, it works well but is very sensitive to proper set up.
A terribly set up DC on a 20ft trailer is useless...a properly set up DC on a 20 ft trailer is a pleasure to tow.
ProPride, Hensley, and Pullrite hitches eliminate sway period. Some trailer designs just tend to sway more than others... Especially when the heavy stuff is in the back of the trailer (bad design)
Overkill is often a subjective topic. It never seems to be overkill when you have to make an evasive manuver or you get hit with a 40 MPH blast of wind to the side of the rig.
Is it overkill to run DualCam on a 20 ft trailer? Not if its set up correctly...
Height and width of the trailer do play into aerodynamics and how much power you will need to pull the trailer through the air. But weight distribution is set up based on the tongue weight and worms to distribute the weight of the tongue weight across the axles.
The hitch shops are asking the right questions...they need to make sure your components can handle the weight distribution. This has to do with matching the Tongue weight to the receiver and the trailer weight with the trucks tow rating. Etc etc
Many people use the E2 on 30 plus ft TT's with great success. They make a 4 pt 400 lb max tongue weight Equal-I-zer that I can use on my pop up.
Remember, a properly loaded, properly built TT, with a properly set up WD hitch will not sway. You will get some movement from passing cars and trucks but this suck and pull motion is NOT sway. Sway controls are there to help make the connection between the TV And the TT more rigid and makes the trailer and truck feel like one unit on the road.
Hope this helps
Thanks!
Jeremiah