I friend had a 4-bike hitch carrier which he used successfully behind his van. No issues whatsoever.
On a cycling trip to the Texas Hill Country, where a group of us were camping together, he towed his large pop-up trailer behind his van. He towed that trailer frequently also without issues.
Being a welder, he added a 2” receiver to back of pop-up camping trailer so he could carry four additional road bikes for himself and friends traveling with him. Bikes were probably around 80 pounds, and total added weight in the order of ~ 150 pounds, with most of the mass at least 2 feet behind trailer.
Anyway, structurally there was no problem, but the added mass at very rear made the trailer very unstable as he approached 60 MPH. It would start swaying uncontrollably as speed increased. Hanging weight at back of a trailer can change towing dynamics in a bad way. This is not the case with a toad.
Due to liability concerns, it’s probably easier for manufacturers to defend broad statements prohibiting use behind any towed vehicle if prohibited at all.
Having said all that, I wouldn’t go against manufacturer due to liability even if I knew it was perfectly OK. They just wouldn’t get my business.
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