First, you may not be able to tow 5,000 pounds, You need to know the maximum COMBINED Gross vehicle weight limit for the motor home and the actual loaded weight (Gross weight) of the motor home.. in my case though the hitch is 5,000 pounds, that second calculation (MCGVW-GVW) (note the lack of the M on the 2nd element) I can only tow 4,000.
Second, for towing you use the actual weight of the vehicle (this will be neither the Max Gross (i hope at least it is less) nor the curb weight, but the full gas tank weight of the vehicle as is is loaded when you travel.
In both cases you need the weight of the vehicle (Motor home and towed) loaded for travel.
In my case the loaded weight of the car is within 200 pounds of the curb weight. But your load may be different.