Easier to take it down to the local tip and weight it.
Yep, and our local metal recycle places will generally weight them too, sometimes for a small fee, or if I'm taking a pile of bottles / cans in they say sure go over and we'll weigh it up
Specs tare / kerb weights are not important, just know your vehicle GVM, get it weighed with normal fit out, GVM - actual weight = payload available (to stay legal).
Be aware of water / fuel tanks, maybe weight with full fuel, then trip parameters can determine and let you add water x *lt x 1kg . . . then other gear supplies.