The nearly complete base. In this photo four sections are attached and three are dry-fitted -- thus the clamps. The target width across parallel sides was 78" and I achieved 78-1/32". Some of the cross-braces described below are visible in the rear section to the right and left of center. Also note the use of pressure-treated lumber for the sill plate and standard lumber for the remainder of the structure. Update 4/20: The base substructure has been completed.