All of what has been mentioned. I prefer weighing all at once, but generally try to time my weighs for when the truck stops aren't as crowded. My last truck stop weighing was perfect- we parked in a pull-through spot, dropped the camper, and then weighed the truck. While my wife went inside to pay and get the slip, I hitched back up and picked her up on my way to the scale. Did the combined weighing, and drove off into the sunset.
10 minutes, tops.
In pictures and words:
http://www.learntorv.com/2013/05/how-to-weigh-fifth-wheel-camper.html