Looking to pull a 2017 2038R on a 10k GVWR 20' flatbed. With an Expedition EL. I've got the big engine, towing package, etc. My rated limit is pretty similar to a F150, just a tad under. Base tractor is 2400lb. With loader and backhoe I'm not sure. For sake of discussion, say I'm at 7k total weight with load and trailer.
Ford does its base ratings fairly low but then has a "weight distributed" rating. I've had experience pulling a 36ft RV with the Expedition, without weight distribution, and it was scary! And it only weighed 6500lb or so. I survived, as did the trailer and truck, but you definitely want WD to safely tow those RVs. My thinking though is that it's not so much because of the trailer weight, but because of the wind and sway effect. Those RVs are a big wind sail. My thinking is that with a flat bed and tractor, the wind really shouldn't be much of an issue. And therefore, probably not much if any sway at all. Without WD things may not be perfectly level, the back will drop a bit, but should I care that much?