[shocker]

Always go prepared. Fully sanitize/flush your fresh water tank and piping. As pointed out, put water in your tank (I learned the hard way to have some water on board -you arrive at the campground only to find that your site's water supply is not available for one reason or another).
Then with your rig loaded up with all of your stuff, go to a CAT scale and get weighed to verify that you are under your rigs weight limit.