.... trial and error.
Don't worry about trying to get your TW perfect ... worry about how the trailer pulls. TH's are very different than RV's in this respect ... the more you load it down, the less the TW, but where you load these weights can adversely affect handling.
We haul a 2011 Streetglide plus 110 gallons of water and gear. With a 200# generator in the tail and the 'Glide against the base of the Murphy bed in a Baxley LA Chock, it pulls perfectly. When I have loaded the 'Glide over the axles, the trailer was all over the road ... not enough TW!
Fully loaded with a full tank of diesel, full tank of gas in the 'Glide and another 20 gallons of gas, trailer spare and full coolers in the bed of the truck, the whole setup weighs 15,760# .... steering axle, 4,160# ... drive axle 4,840# ... trailer axles 6,760#. The truck weighs 7,580# (GVWR - "red" sticker) and subtracting the weight of the diesel and cargo in the bed, the TW calculates to 904#.
The truck is a 2015 Silverado 2500HD Double Cab Duramax 4WD with a WD hitch and the trailer is a 2013 W&P 18EC as in my sig.
White 2016 Work & Play Ultra 25ULA, Cherry Wood, Pebble, Onboard Onan 5.5, Onboard Fuel Station, 50-Amp Service
Onyx Black 2015 Chevrolet Silverado 2500HD DCSB, 6.6 Duramax/Allison, LTZ/Z71 397bhp/765t
Shadow Black 2016 Ford Mustang GT Premium Convertible 435 bhp (Wife's Toy)
Merlot Sunglo 2011 Harley Davidson Street Glide FLHX, FM 107", PM Heathens 21"/17", Metzeler ME880's (200 Rear), 115rwhp/124rwt