Your profile shows you have a 5th wheel not a motorhome. If you've changed to a motorhome more information would be helpful. If you now have a class A or C gas powered motorhome the maximum towing capacity would be 5,000 lbs. Many models only have a 3,500 lb. towing capacity.
Tandem tow dollies generally weigh between 800 lbs. and 1,000 lbs. The car itself weighs between 3,300 lbs. and 3,600 lbs. depending on year and options.
A jet Ski weighs in the neighborhood of 800 - 1,000 lbs. The combination will run in the neighborhood of 4,900 lbs. to 5,700 lbs.
If the combination is on the lighter side it's touch and got for a motorhome with a 5,000 lb. towing capacity, and a definite no go for one with a 3,500 lb. towing capacity. If you have a DP with a 10,000 lb. towing capacity it shouldn't be a problem
Hikerdogs
2013 Winnebago Adventurer