To do it right,
Load the family into the TV and go to the scales. You want to get front axle, rear axle and total weight.
Then, go home, get the trailer and go back to the scales, repeat step one but this time add the trailer only. You now have the TV weight ready to camp minus the trailer and including the trailer. Last step could include unhitching the trailer and weight the tongue only. But in reality I have always driven the TV over the scales some time when I was near one. And on a different occasion weighed the loaded rig, front,rear,gross TV and trailer axles. And been totally comfortable with my weights. I have done it several times, and they have always been pretty consistent, so no big deal to me any more.