I hear ya. I use the same technique, which I also learned here in the forums. I also really appreciate the fact that I don't have to lug weights around with me.

I use two NRS Tuff Sack Medium Dry Bags that are 22 liters each. Each one filled with water on site equals about 42 pounds. They are too big to go into the hull, so I just throw them in the foot well of the front passenger area.
The first time out I used both bags, and that actually seemed like too much weight. The bow would actually plunge through boat wakes rather than ride over. So the last couple of times out I've just been using 1 bag.
Seems like the optimal weight might be achieved by filling both bags 2/3 full, but 1 bag is just simpler.