Well that is were the problem is! Many people have never actually weighed their trailers and they simple read the manufactures specs for "Dry weight" but fail to understand that many items are not included in that weight - especially any optional items. Items common on the older trailers not included on the manufacture dry weight include things such as AC, Propane
tanks, batteries, awnings, fridge
, stove, hot water tanks, showers, toilets.... the list goes on...
Good news is over the past few years some of the manufactures are starting to give a stated leaving the factory weight. Which IMO is much better.
A good rule of thumb is to add another 500lbs of weight to what ever the actual finished trailer weight is to cover all your personal items, clothing, bedding, towels, hoses, chairs, BQ, dishes, pots and pans and food etc in the trailer. If you ever take everything out of your trailer and weigh it all you would be surprised what it all adds up to. A friend did this a few years ago & even though they thought they had the lightest of products in the trailer, lets just say their trailer went on a *serious* diet after they weighed everything.
I do weigh my trailer fairly often and at the end of every year anything that didnt get used over the last year gets taken out.