This combination may work for your rails to make them less brittle ---
Go here for a glance at the full list :
http://www.jamestowndistributors.com/us ... &page=GRID
Mix the epoxy with some WEST System 404 High Density Filler.
Then add a bit of ---Milled Glass Filler--- ; this keeps the matrix stable.
Then add 5 to 10% WEST SYSTEM 423 Graphite Powder
(i make my own by sweeping up the black stuff any time i sand on anything
made with carbon & epoxy)
Play around with your own proportions by mixing several combinations
smash each with a hammer.
This is what we used to bond the spars on my Rigid-wing HG to
the carbon skins ; it Never broke and the engineer said it was good for
Ps : You now have a Really NASTY item to sand on ; i "Always" use
wet/dry sandpaper or steel files AND water so the dust can't go airborne !!!!!
A dust mask simply is NOT good enough (.)
PLEASE don't go Macho without the water ,
your lungs will HATE you