Fred - Yes, I have experimented while building and can say without doubt that I have actually saved weight with Epoxy/glass laminates. The two fuselages shown are for similarly sized planes. The horizontal tails for each were finished differently. The older one's stab/elevator was finished with doped CF veil on the Stab part and weighed marginally more than (about the same as) the one finished with glass and epoxy. The glassed one is stiffer. That is because the glass took less epoxy than the amount of dope needed to fill the veil. Dope weighs less, as far as I can tell, but I seem to need more of it. My original primary Force fuselage had more, but lighter balsa (really good 5-lb stuff) in it than the fuselage shown being built (7-lb +/-). When finished with dope and the newer (lousy) silkspan, the original PF fuselage weighed 4.6 ounces more than the new one. I believe this is because successive coats of dope raised ('floated') the silkspan, as more coats dissolved the earlier coats, and I ended up with more dope than I should have needed. The epoxy, applied as I described, kept the glass down against the fuselage surface, so that only enough to fill the fine weave was necessary to bring it to a smooth sheen, without grain showing. I'll attach a picture I took of the new fuselage against the original P-Force plan so that you can judge how mush less balsa I used, but remember that the P-Force did not have the cowl-cheek tripler.
Bill - I used West Systems 105 Epoxy with 206 hardener.It has a reasonable working life, but becomes too viscous, if you take too long getting the surface coat on and scraped thin (almost invisible) and glass oriented and rolled out.right. That is, you have to work diligently an quickly before the viscosity works against you. Time? H-m-m-m-m,...maybe 10 minutes of thin enough viscosity. The stuff is usable for other tasks for a longer time, but we're trying to save weight here. I wish I could remember this better, but I'm only talking "ballpark" figures, when it comes to workability for this particular task. I like this resin, but as I said, it can become a real mess, without precautions. If the resin is left unevenly applied, work is multiplied in getting the finish right.
I agree with Paul on profiles, but have to say that this particular trussing took minimum time to make (just time to scroll-saw the opening, cut and white-glue the diagonals), except that laminating three pieces (two 1/16" sheets on the 1/2" core) to make the 5/8" thick fuselage takes more time. However, using 1/16" plywood for the nose makes a seamless transition along this significantly stiffened fuselage. Don't underestimate how much torsionally stiffer these few simple diagonals alone make the structure, especially when the box is completed with the sheeting. Even the small opening saved significant weight in the right place (I weighed after each step).
The 1/64" plywood route makes a VERY stiff and torque-resistant fuselage, but that great stuff is much heavier. That''s something you can compute ahead of time in your decision making.