That must be a C-Max hybrid at only 3000 lbs. My C-Max Energi is 3800 lbs and I tow it on a dolly (+another 100 lbs or so) behind our Axis (E-350) without an issue (I've weighed the Axis and have plenty of "room" to tow the C-Max; my limiting factor is the 5000lb factory hitch).
If you really want to be sure about the weights: take your RV to a scale and weigh it loaded as you will travel. Then subtract that value from the GCWR the result will be what you can really tow.
That question was recently discussed. With only a few dissenting views, most of the comments said you definitely do need a supplemental braking system. Either a Brake Buddy type or one mounted on the car (my personal preference).
Bad decisions make great stories!
I have a Thor 28z, E450 and tow a Honda CRV (3600 lbs.) with a brake buddy stealth, Blue ox hitch, 4 down and have NO problem at all. Hitch is rated for 500 lbs. I think is you have your weights accurate and your vehicle is towable, 4 down, you should be OK.