I know the game of not knowing your weights at the load site all too well, I run a quad axle dump trailer and if we're doing a demolition job or a contaminated soil move, it's port to port so we don't know our weight till we hit that landfill scale. Thankfully most of our dump wagons are air ride and have suspension pressure gauges so I can do the same basic guessing, and you get pretty accurate with it after a while. Good thing too since we're only allowed a 3% over gross tolerance, so I can take roughly 120k and still stay legal, but sometimes the DOT guys will still give you the stink eye if you're over 118k.