Nice job on all the research. I am somewhat suprised that it added this much weight. The latex stuff is mostly water and as it cures the water is released. I am wondering if you had let each coat dry more if the weight gain would have been less? You could always use the traditional balsa wood sealers but they stink! I have read where others have used hardware store brand wood sealers with success. You can always add density to the filler by adding baby powder. An old trick and it does not take much at all.
