Your tow limits are determined by the Sprinter chassis. The chassis alone can carry 11030 pounds. (GVWR- Gross vehicle weight)
It's total combined weight of the chassis and the tow vehicle is limited to 15250#. (GCWR- Gross combined weight)
You can see if you are at 11030 # your tow vehicle can only weigh 4220#.
My Siesta Sprinter is also a class C on the MB 3500 chassis. I weighed my RV when new, only full fuel and propane and a driver. Otherwise empty. It weighed just under 9975# so I have a 1055# carrying capacity. Weighed again with full fresh water and fully loaded to travel, I am at 10810#
I also have a 5000# hitch and the Suzuki weighs 3400# so I have some latitude in the tow.
You need to weigh your RV, fully loaded for a trip. Water, fuel, propane, clothes, tools, snacks and people to get an accurate weight. (primarily to insure you are not over the GVWR 11030#)
My neighbor and I installed the BlueOx baseplate on the Suzuki, their instructions are easy to follow and are available on their website. Trailer Hitches, Trailer Hitch Bike Racks & Trailer Hitch Accessories | Hitchsource.com | HitchSource.com
The baseplate will cost about $400 for the Fiat and having it installed will be another $700-1000 including the electrical.
There are several base plates available, I'm only familiar with Blue Ox.
I hope this helps...