I just insalled my sway control....I did drill 4 holes in the frame of the Scamp
(not in the same places as on the plate since they were way too close to the top and bottom of the frame). I really don't think that they will effect the structual strength of the frame as there are just 4 and there is plenty of frame left and they only penetrated one wall. The frame was surprisingly heavy guage metal.
The question I have though is: Does anyone really disconnect their sway control when it is raining, or is this really not necessary? And, how tight do you tighten the "on/off" bar when ready to tow? It is my first experience with a sway control, but I will enjoy the extra security. I also installed a transmission cooler on the Nissan Quest for the same peace of mind. It is very easy to install yourself and it only cost $58 with shipping.