Knowing the tongue weight is half the battle, and for about the cost of going to a scale you can make your own tongue scale. Two 2x4's about 7' long, two short pieces of pipe, 1/2" copper pipes a foot long work, a patio brick, and a cheap bathroom scale from walmart. Put a mark every foot on the boards after screwing them together, place the 1 foot mark on a pipe on the brick, the tongue foot on the 2 foot mark, and at the 4 foot mark the other pipe on the scale. Zero the scale then let the trailer fully down on the boards until it is level, Multiply the scale reading by 4 and you have your tongue weight.
Now that you have the actual TW, setup the WDH so that the truck sits the way the manual tells you it should by measuring the wheel arches. Knowing what your truck weighs with you and a full tank of gas, and knowing the TW, you should be able to figure out the weight distribution easy enough.