I'm sure you'll be fine. I tow a loaded 20ft enclosed all over with a gas standard cab 2004 Hertiage F150. I'm probably pulling between 5000-6000 lbs total, car weighs 2600lbs. I have helper air bag springs as my only modification and it works great. It'd not work nearly as good if my trailer brakes didn't work.
Yes, I know the trailer is there, but it is safe, reliable, and I've had no troubles thus far - knock on wood.