I pulled a Grandee (8'4" x 7' 7" - 900 pounds) on trailers like this. I rented one from Uhaul which was just like this. Uhaul called it a garden tractor trailer.
Set the spa horizontally on the rails, snug it up against the ramp and tie it down with 2" straps or better - the kind with the ratchet winch. I ran two straps from the handles on the ramp to the front rail - the spa and trailer became as one.
The spa sits low, you may be able to see over it depending upon how high your tow vehicle is - if you put this behind a moving truck/rental truck you might forget it is even there.