The best way to know for sure is to tow a boat similar to yours during the test drive, and to have a somewhat challenging course planned. Since you don't yet have a boat or an adequate tow vehicle yet, soliciting help from a friend with both items would be in order. New vehicle sellers will probably not allow towing (because the engine and brakes aren't broken in), but it should be fine for a used vehicle.
Most dealers will allow you to take the vehicle for a few hours, or even overnight, if you seem very serious about buying the vehicle regardless of new or used. Take it home, hook up your boat, and go tow it around a little. They don't even have to know.