Clint,
When I came back to Stunt after a 20 year layoff I had trouble building a D Tube wing from a kit. Same as you, I could not figure out how to block the leading and trailing edges to get every thing straight and level.
Lucky for me I discovered Tom Morris's system for wing building. The first panel I built, ended up as scrap.
But after that small learning curve, I can now build a Straight, Level, Strong, Light weight wing for very little money.