I had a Laser and sailed it for many years, loved the boat. Switched to Windsurfing though since it was faster and more fun.
In my EV and air spring work under the rear of the Insight,I got quite familiar with under there.
I think that a trailer that was tied to the frame with a secure attachment as Yves did with his hitch would be much better than a roof rack. The balance of the boat position relitive to the wheels determines the tongue weight. As Dougie says there is no reason it has to be over 20 lbs, and at that weight, it is less weight on the rear than a bag full of can goods from the store. The trailor and Laser would fall into the shadow of the Insights wake with a trailor, for better drag reduction.
There is very little side force on the car when cornering with a trailor that is balanced well, and the pulling forces would transfer to the frame in it's strongest direction. On a roof rack, the 130 lbs way on top of our lightweight cars, would present both a much more substantial arodynamic drag. and much more tipping force in cornering, as the CG would move up. I would also worry about the wind effect that John mentioned, A good gust, and you could be on 2 wheels, and of course you would not be going sailing if there was no wind.