Here is a link to an excellent website that will help you tremendously....
http://fifthwheelst.com/
When you click on the link above and the page opens, look at the top of the page and select the "4 Step Weight Safety Plan". The dropdown list will show four steps. Start at step one and go through at least three of them, and probably read the fourth step to make sure that your tires are up to the load range/capacity that they need to be.