I would echo Dom’s suggestion of considering hiring when you need it, if its just going to be occasional towing, or you need that type of tow vehicle for other purposes. 3.5t towing capacity is a must – by the time you have the boat and gear, trailer and yourself you will not be far from that. And it is the stopping and cornering, not the pulling you need to worry about. The running costs on suitable cars are much much higher than a large estate or even a 2wd SUV.
I have had two Discoveries and a Touareg – all very competent tow vehicles, all very expensive to run.
My problem was that there were no hire companies in Norfolk with suitable ‘casual’ hire vehicles that I could conveniently rely on. However I know that Laurence hired an excellent car in Dorst to pick up Joann earlier this year.

But of course suitable tow vehicles do also make commanding everyday drivers……