I agree with everyone so far. Load the TT correctly balanced.
Don't confuse sway with the push n pull of overtaking trucks (thats normal)
Look at all the enclosed 30-35 ft (5000 lb) ATV/snowmobile trailers being towed direct to the ball without a WD hitch or sway control. Year after year and many thousands of miles.
We just returned back home from a (steady 20mph with 30mph wind-gusts) 500 mile tow using a 3000 lb loaded enclosed v-nose trailer direct to the ball using a 1500 truck with the truck bed also loaded up. Because the unloaded truck sits rear end high with a max tow package, the combo towed level once i hitched up with a 1.5" squat. No issues at 65-70mph. I had to do a minor headlight adjustment. It towed flawlessly. My DW towed it for 150 miles and she loved it.
MY TT:
The transporter who towed my TT half way across the country from the mfg to the dealership towed it direct to the ball using a dual wheel 350 truck. NO WD hitch and no SC.
Im towing a Jayco 23 RB (27 ft) @6000# wet with approx 800# TW (its 100# more when i bring the bikes on my tongue mounted bike rack, see my profile pic) with a max tow pack silverado 1500 with a Pro series Reese and friction sway bar.
I've tried the system both ways to see how it tows. So far (about 5k miles) i have not noticed any difference with or without the sway bar.
I also tried this same 6000# Jayco using my beefed up 2500HD and it it towed perfectly direct to the ball as well as using the WD hitch which i didn't feel any difference in the tow. Wheel well measurements were also in check however, it did squat a tiny bit in the rear but not enough to feel any towing difference or affect steering.
I did have 'Tork-lift adjustable Stable-loads' on my helper springs which engages the helper spring earlier than normal (without a load).