To boron or not to boron, that is the question. If you boron, I recommend the .004 stuff rather than the .003 stuff. The .003 stuff is about the thickness of your hair and is not as stiff. It also snaps into tiny pieces a lot easier. Always tape the edges of the boron rods to the building table. Trust me you don't want to get a piece in your foot or hand. You can google all the hazards (and techniques), but expect a trip to the emergency room if one snaps off inside your finger or foot.
I did find that the .004 is much easier to work with, easier to see the pieces and provides a stronger structure. Its applied with DUCO cemented, thinned about 50 percent with acetone. Its 30 percent heavier than the .003 stuff, though. You can expect to add a couple to 3 grams to the model if using boron, but this stuff is incredible If you get a piece of 1/32 square and put it on two sides its got the same stiffness as a piece of carbon rod but at about 1/10 the weight. Speaking of weight, this is optional but for $20 you can get a milligram scale. Make sure its to a 1/1000 gram and not 1/100 of a gram. We got a scale for F1D to weigh the components while Joseph built that 1.4 gram model (yes the whole plane ready to fly excluding rubber band weighs less than a gram and a half). I will see if I can go the route of non-boron plane for this build. The balsa is very fragile so you have to build a foam box to transport the plane. This is really not a big deal as we'll get to later.
P.S., in case you are wondering what it costs, 100 pieces of 24 inch long boron rod costs $17. That's 17 cents a piece- pretty cheap, but it takes quite a bit of patience and technique to apply. I can cover that if I go that route. The end result is a structure that is incredibly stiff. http://www.indoorspecialties.com/index1.html