What matters, in the end, is the load seen on all tires of the combined rig. Remember that we are using static values as a stand-in for dynamic forces when underway. They are not constant -- these forces -- once one is moving.
The differences from  solo (both vehicles); to  hitched together, but without WD applied; to  hitched with WD applied. Getting persnickety about a few pounds won't help much.
TW is more easily deduced from scale passes than otherwise. A SHERLINE gauge is a tool, and an inexpensive one. "Close" will be good enough, overall.