Pulling a boat - hitch & ball mount w/rise Q

After you get the receiver mounted, I would eye-ball it closely. compare the height of the receiver to the height of the trailer axle. If the end result ball is too high, it will cause the back end of the boat to nearly drag on the ground.

 

1) Install the hitch receiver and wiring for the lights.
2) Ask the boat dealer how high the boat trailer hitch coupler is off the ground when the tongue is level. Also ask what size ball the coupler needs...1-7/8" or 2" diameter.
3) Do the arithmetic and figure which hitch ball mount size you'll need. Buy the ball mount and the ball. Be sure the ball shank is the same diameter as the ball mount hole. It's better to have the boat trailer sloping down toward the car an inch or so if needed than to have it sloping upward.
4) Or, buy both ball mounts and bring them, the ball, and a suitable wrench to the boat dealer when you're ready to pick it up. Use the one that fits. Return the other; don't scratch the paint.

Here's a tip for tightening the nut on the hitch ball...slide the ball mount into the receiver so the ball points to the right, not upward. Screw the nut on, put the wrench on the nut, and stand on the wrench. Easy way to tighten the nut. Put the ball mount into the receiver pointing left to loosen the nut by standing on the wrench that way.

 

^ that. Without measurements you're nowhere. And if at all possible do the measurements yourself- this is not the kind of thing where you want to trust some salesman to guess and then you order parts or commit to a schedule for a boat trip because you're likely to find something was missed.