



Here are photos of the hitch extension I built in 12 years ago and am still using on our 2006 F350. Its made from 2-1/2" X 1/4" wall square steel tube. I believe it is about 22" to 24" hole to hole. I have towed our 7,500 lb car hauler many 1,000s of miles with it.
The new extension will be longer, 30" to 36" and will be made of 3" X 3/8" wall steel tube and have similar side chains/turnbuckles. I agree that 1/4" wall would be plenty, but I will likely use 3/8" so I don't have to think too hard about it. The trade off for added strength is cost and weight.
I agree that 500 lb tongue weight seems low for a 7,500 lb trailer. But I'm pretty sure that is what it is. I remember weighing it when I was setting everything up, but that was 12 years ago and the remembering part of my brain ain't what it used to be. I was trying to keep the tongue weight as low as possible to reduce the torque on the hitch, but still have stability on the highway. It was easy to adjust the tongue weight by just positioning the jeep fore or aft on the trailer. I still have the two walmart bathroom scales I bought to weigh it.
I love the WD hitch set up we currently have. The truck actually drives much better on the interstate with the trailer than without.
The added leverage on the receiver hitch is my main concern. When the weather clears up, I'm going to crawl under a 2018 and check the side plate thickness and thump it with a small ball peen hammer.