This is an interesting topic for me, Diamonback, as I've had similar experiences. I've got a 5x8 utility trailer that is really too small for the Gator XUV, my tandem axle dump is a 6x12 and it has ramps and welded in D-rings in the 4 corners of the floor for hauling equipment, but it is 3500 lbs empty and there isn't much room for convenient strapping down of the Gator. I've also got a 17 ft. car trailer which is way bigger than necessary, but is nice and low, tows easily, and my favorite choice. I've thought about getting another trailer that would better fit the Gator but I just can't justify it.
I'm thinking that your 18 ft utility trailer might be more heavy duty if you don't want to use it for your Ranger, because my experience has led me to conclude the big trailer is actually easiest and best for me.
If you do go with your dump trailer and have D-rings welded in the floor, run your straps from the front rings to the rear of your UTV, and the rear ones up to the front, and I think you'll find you can crank the ratchet straps down in such a way that it won't move forward or backward and rub.
Good luck,