When entering numbers into the demonstrator, you should add some weight for the options you have added to the trailer, as well as some weight for the cargo you'll carry in the trailer. Trailer options can easily add from 250 to 500 lbs. to the trailer weight. Cargo weight in the trailer can add as much 800 lbs. Don't forget the weight of full propane tanks, the weight of the fresh water tank (if you insist on towing a bunch of water around,) and so forth. Here are some examples of weights of things you might carry in your trailer:
Figuring most RVers travel with at least two bikes, that's 316 lbs. right there, without the clothes washer. We haven't even added personal clothing and other personal items, yet. Don't forget the weight of CD, DVDs and VHS tapes, either. CDs and DVDs weigh about 4 oz. each. Not much, but 50 of them weigh 12.5 lbs. Let's not forget books and glassware, either. Wood doesn't get much lighter when it's made into paper for books, and sand is still heavy after it's turned into glass. Another good reason to consider plastic cups and tumblers.
Finally, don't forget that somebody has to drive the truck and ride in it, too. Two adults with minimal personal effects can easily put 350 lbs. or more into a truck. That counts against the Available Truck Payload. When using the calculator, make sure you leave enough Available Truck Payload for you and your navigator.
After entering numbers the first time, you can play "what if" games by changing the cargo and options weight, without having to re-enter all the numbers, and clicking the "Demonstrate" button. For that matter, you can change the truck and/or trailer numbers and click the "Demonstrate" button to try different truck/trailer combinations.
Before using this demonstrator, be sure to read the legal disclaimer at the bottom of this page.
Legal Disclaimer: This calculation demonstrator is intended for demonstration purposes only. It is not intended as a device to select the safest and best combination of tow vehicle and trailer. Do not use it for that purpose. You still have to use your own best judgment in selecting the best and safest combination of truck and RV. You still have to use your own best judgment in using a certain combination of truck and RV. If you use this calculation demonstrator for anything other than its intended purpose of demonstration, neither its author nor the web site it's posted on nor the owner of the web site it's posted on nor the owner of the hosting service of the web site it's posted on is responsible or liable for any damages or injuries resulting from the misuse of this calculation demonstrator.