Tom, I don't know that it would be accurate enough for a Champs, but it is a quick(ish) way of getting some idea of weight.

Two scales (preferably the same) one under each hull at the balance point (just at the front of the plate cases on the Stealth). You can 'trim' the balance with loose items such as daggerboards and rudders. On the day I did mine there was a bit of a breeze and the boat was moving around a little bit so a still day is best.

As you probably know, you just add the two readings. I took about four attempts before I felt the boat had been settled enough to trust the readings. That's when I got the 56 and the 60.