[MikeMoller]

You could get weighed at a scrap yard or lumber mill yard. Load the car on the trailer and weigh the whole rig, go unload the car and go back and reweigh the rig, the difference is the car weight. It will get you in the ball park, those scales around here are state certified on a regular basis and I have found them to be pretty accurate. Might be able to do the same at a truck stop with scales.