I pull a 24' 10,000 lb enclosed trailer, hitch rated at 15,000 lbs and 1,500 lb tongue weight.
I would recommend getting a Sherline Trailer tongue scale, Sherline Trailer Tongue Weight Scale - 2,000-lb Capacity Sherline Tools 5780
With 7,000 lb rated hitch, you will be within rating if your GCWR is ok. You will also have to watch your tongue weight, I would discuss with reputable trailer hitch company assuming you have a 700 lb tongue rating.
One option may to back your Miata into the trailer and keep the engine weight on rear trailer axles or behind the axles.
I use weight distribution bars, and did on my previous coach as well. The air bags will handle my load, but my belief is that it rides better with the bars. I have read and followed the Trailer Toad concept of removing almost all of the stress of the tongue weight from the coach but haven't went that route. More importantly to me than the distribution bars is the sway control, really helps in the wind and around other high profile vehicles.