GVWR for older travel trailer
You need to know the GVWR for any trailer you are going to tow. If you happen to overload it, you risk excess wear, breakdown or accident. And then you have extra risk from lawsuit.
The 2 places I've seen it was on a plate fastened to the toungue, and on a label inside one of the cabinets. If you can't find the official GVWR for a trailer either on the trailer or from the manufacturer, don't buy it. Weighing it empty will let you know the 'dry' weight, and if you are careful about what you put into it you can avoid overloading your truck ratings. But you can only guess at the GVWR for the trailer and the penalties for guessing wrong could be unpleasant.