You would probably get better answers on the Motorhome or Dinghy towing forums.
Now, I am not a motorhome guy and they may use different terminology.
Are you talking about Hitch Weight (The amount of weight the hitch is rated to carry)
Or are you talking about towing capacity,(the amount of weight your MH is rated to tow?)
If you put your jeep on a dolly the weight on the MH hitch will be maybe 5 or 600 lbs.
The weight of what you are towing will be 4200 for the jeep and whatever the dolly weighs.
If you are towing 4 down the weight on the hitch will be ten pounds or so
your towing weight will be the 4200 of the Jeep.
You must know exactly what you are talking about and you need to use the proper terminology.