With towing 4K you would really consider weight distribution AND airbags AND sway control, as you may have in excess of 500# tongue + cargo weight on the rear axle. With rear bags/HD bump stops only and that much tongue weight, you'll be effectively removing load from your front/steering axle which can induce understeer. I have towed that much without WDH (airbags only) and it certainly can be done (and will feel decent unless you need to make a quick turn), but recently went back to using a WDH for our camper and find the rig is more stable (to the point of almost forgetting the camper is back there). For towing rental trailers (like with my tractor), it's hard to set them up with WDH so I run airbags only.
FYI my current setup is below - Firestone bags at 20 psi, basic chain style WDH, and sway bar (not hooked up in this photo). The camper weighs about 4,000# loaded and has a unloaded tongue weight of about 530#. We've towed it at least 10,000 miles including all the way to Montana and back from MO. We just pulled it to the Gulf coast and back and it was a very low-stress towing experience.
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