The GVWR of the trailer should be on a metal plate on the outside of the trailer. There should also be a sticker on the inside of the trailer (either by the door or in a cabinet) that lists the actual dry weight. If you use the GVWR posted on the outside of the trailer, you can figure 13-15% of that number to be a max tongue weight. This would actually be more accurate than a dry brochure weight somewhere. If you want an actual weight, you can always use your current TV and go to a truck stop and weigh on a CAT scale. This is very simple, put the truck on the first scale, the trailer (loaded as it would be for camping)on the secondscale (or if need be 2nd and 3rd scale), disconnect the truck (with the tongue on the trailer scale) and get a weight. reconnect quickly and pull off. (I would not do this during a busy time). This will give you a weight for your trailer. It is not an accurate way to measure your TW but again, you can take 13-15% of the # you obtained on the scales. It costs around $9 to weigh and you can reweigh for $1 for 24 hrs after that. Bring something long like your window scraper, a broom handle or something so you can reach the button to push for the attendant.
http://catscale.com/how-to-weigh