I seriously wouldn't do it. You also have to consider the stability of
your car with the boat under tow. plus the cars brakes. I have an 18
ft
Chris Craft fiberglas with a 140 mercruiser IO on a single axle
trailer, and I tow it with a Mercury Grand Marquis simply for the
factor that it has a 5.0 (302) V8 and good brakes extra-heavy
transmission cooler . But still, at a road speed of about 60 mph I need
to pull it with out the overdrive due to strain on the transmission.

My boat isn't really heavy,and I know that is a relevent term, but my
wifes 2003 Chrysler town and country van is rated for a 5000 lb towing
capacity, and I wouldn't even think of towing the boat with her van.

Also you must rememebr ramping the boat/trailor. going into the water
is one thing, but coming out with a boat is something else. all your
weight is shifted to the back and under load. thus you have less
traction with your front wheels, and especially on a wet ramp this
could be big trouble! like...sliding on down and submerging the car.

I know you're trying to be optomistic, but look at the hard facts.

your car is way to light!

Tim