Two summers ago my BIL rented a TT for a trip. Dealer said he "didn't need" a WDH/anti-sway. My BIL questioned why I used one with a similar trailer?
I kept and eye on my mirrors, knowing that he was not familiar with towing. He was definately fighting more than I was.
Half way thru our trip, even his novice eye could see how stable I remained, while he bounced (porpoised) and swayed when we encountered rough roads. He said he was watching my trailer to see what he could expect...noticed real quick that I stayed more stable than he was.
Get the anti-sway.
Only adds a couple seconds to hooking/unhooking....saves hours of aggravation.
EDIT: BTW, I tow with a 2013 Ram 1500 (reg cab, 8' bed, HEMI). Smaller trailer, only 19', 3500# GVWR.
I currently have 300# of sand bags in the bed, I don't know it is there. But I won't tow that TT without WDH/Anti-sway. It is not about the weight, it is about the porpoising and sway that can happen at that hitch point (because of that weight/length--pivot point).