Ira,
This is NOT hi tech. NO spreadsheet. Just lots of work. The only way to explain what I'm doing is to show you and then explain it.
Under all that mess is my chassis, sitting on 3 concrete blocks. One on each side about where I think the axle should go, and one under the tongue at the coupler.
First, I placed both sides on the chassis, facing the right direction, but both in the same position. but, I weighed and balanced that load on the chassis, so that it weighs the same on both sides.
Today, I bought 7 sheets of 5mm luan and 11 sheets of 1/8" paneling. I've rough cut all of the pieces for the outside skin (front, back, top) and the inside paneling, and placed those pieces about where they will be installed, relative to the length of the cabin.
Next, I cut all of my spars and placed them on top of the paneling, aligning them with the notches in the sides. Everything placed on top is centered from side to side for weighing purposes.
The cardboard box near the back are my windows that came today from Grant. Tomorrow morning, I have to calculate how much cabinetry framing there will be and simulate that weight on the pile. Next, stick my AC unit on the back, the door in it's place, and put a couple of concrete blocks on the front to simulate a biga** battery. And, I'll put a few things I know I'll be taking camping (folding chairs, tables, etc.) where they will be stored for traveling.
The seat/bed cushions should balance out the stuff I'll have in the galley cabinet, so that's a wash. The main storage compartment should be over the axle, so not a concern now. The foam insulation is so light, that I'm not worried about having it on to be weighed. It is distributed all over, more to the front than rear, but very little weight to be concerned with.
THEN...and only then...will I be ready to weigh it and locate the axle point to get my 12-13% tongue weight.. I've explained that process often enough, so most of you should know what I'll do. I'm going for 12%-13% tongue weight for the axle placement now. If the total weight turns out to be lighter than I had originally estimated, I'll go for more tongue weight...maybe up to 14% now. If it varies a percent or two in either direction when it's loaded for camping, It should still be in the 12% - 15% range.
Any more questions???