You can get a tongue scale online at Amazon for about $140 all in. Not a bad thing to have if you're close to your payload numbers, and it will always be worth $75-$100 used if you want to sell it. For a big trip it's nice just to slide it under there and see where you are at...."oh, I have 200 lbs left, I'll just throw the firewood in the bed"....or "That's close, maybe I should put the charcoal under the bunks".
Some will say if you're that close that you don't have enough truck.....I say no matter what your weights, towing rigs like these takes planning and weight and balance. Every semi does it, every airplane does it. Even if you had an 1 ton, you STILL want the trailer properly loaded. Sway is sway and the trailer doesn't know anything different than it being pulled on a ball hitch....whether that ball is connected to a 1/2 ton or full ton.