My 13’ Scamp
never sways with passing semis. A slight tail waggle sometimes with a speeding tour bus- they’re the worst- but not dangerous. We run about 12% tongue weight
with nothing heavy at the back.
17 is regarded as one of the more stable molded trailers, so I'm sure you’ll be fine. If you want to add a friction sway control bar as an extra measure, there’s certainly no harm, and they’re inexpensive. If you want to spend some money, Anderson makes a lightweight weight
distributing hitch that integrates sway control. Overkill in my opinion, but if you want the extra security it’s an option.
Correct loading with adequate tongue weight
is the best sway prevention- the Casita 17 tends to run a little tongue heavy- along with keeping speed down and using trailer brakes