Personally the rules of thumb about a bumper pull COULD be modified to 5w trailers also. But add in another about 4-6' for being farther forward over the axel vs behind x amount of inches. Or as I also mentioned, heavier chassis rigs can handle longer trailers vs lighter ones.
BUT, we are now into how big/small one can go, going by chassis strength if one will call it that. Then one needs to power it according to how and where you will drive the rig too. Reality is, choosing a given tow rig for a given trailer needs to have MANY factors/rules of thumb to come up with a proper tow rig for any of us. What works for me, may not work the person reading. When I had kids. many would say a 6500 lb trailer could be towed by a half ton. Well, by the time I put 4 adult sized teenaged kids, spouse nd myself in a typical half ton crew cab, I was at gvwr with 1200-1300 lbs of family wt, add in the dog, 150 lbs including crate, hw, rack, canoe, a bike or two or 6.....I needed some 3000 lbs of payload in the TV. That my friends is NOT a half ton twuck! A SW 350 or 25 series truck yes, but not a typical 15 series truck ability.
Marty