Agree with Michelle, 4 down could be an issue. It didn't work out for this guy:
According to the thread in the FJCruiser site (The owner is also an FJCruiser fan), this happened shortly after he hooked up for the first time. The buddy said the Jeep just started whipping uncontrollably behind the 5er, then rolled multiple times before the driver could pull over. The Blue ox tow bar never let go.
I think the swing in the back of an RV is too much for towing 4 down and expecting the turn to move the front wheels. A tow dolly might have done better, but I would prefer a trailer with mid axles so it can pivot.
I couldn't ever tow that much anyway behind my 3000/300 factory hitch, but I would be willing to try a Polaris Ranger on a trailer. I know several folks that do it with 5ers.
