Dan,
I used to pull my 18' aluminum bowrider with my minivan and yes it can be done, but not safely or efficiently. If you are putting it in the water in the spring and taking it out in the fall then you could manage. However, if you fish (and trailer the boat a lot) by the time you start to see any issues it will be too late. I now have a 6cylinder 4.0L 4x4 and it does not have to work as hard and is awesome at the launch regardless of how shady the conditions are.
Keep your hooks sharp!