Not sure about balsa, but in full scale the first coat of dope on the airframe improves adhesion of the fabric, a glue of sorts, and yes each coat of dope adds weight. on an airframe the size of a gillows kit weight could would be small. perhaps shaving or sanding a little wood from the under sides of stringers and the face of aft bulkheads or lightening holes in the bulkheads during building could make up the difference. What do you think bill?