If you have a bathroom scale have a kid stand on it take his weight hand him/her a bike and go adding all the stuff that you want to carry in the RV, deduct the kids weight and you have that actual weight, you will see how much stuff really weighs, and then start eliminating all that is not really needed.
Also have the wife stand on the scale as every member of the family.
NOTE: when you are going to have the wife stand on the scale recalibrate so that it is 10 pound less, you do not want to sleep in the dog house for a few nights.
Once you have all the weights you can pack the RV so tha most is between the front and rear tires to distribute the weight rather than having an imbalanced unit.
navegator