Chris has a good point re. the properties of epoxy if it hasn't been post cured.  The HDT (Heat Distortion Temperature) of the prepreg will be quite high since it is a 260 degree cure system but our room temp hand layups are typically not post cured.  As an aside, the HDT is normally close to but below the Tg (glass transition temperature) of the material.  It is normally a moot point however since the plane will post cure itself out in the sun on a summer day.  You can also do a poor man's oven by covering your part to cure under a black tarp under the hot sun.  Just make sure it's aligned properly and not stressed!  Maximum crosslink density may be years down the line but the cross link density will increase with more heat.  The more important part is that stress should not be applied when the epoxy is above the heat distortion temperature, (either before or after post cure).  The problem is that without post cure, the HDT will be lower than stated thus the physical properties will be less than optimal.  The Jeffco we use for laminating has an HDT of 190 degrees F if I remember correctly.  So given a few hours in the sun in the summer, the Jeffco should cure to it's maximum cross link density and give it's stated HDT.

I will probably go with a toughened epoxy with a higher HDT but there are certainly a lot of successful planes out there with Jeffco, however I would like to have better fatigue and peel strength, all properties of toughened vs. non-toughened systems.  BTW, Jeffco does make toughend epoxies.

Dan Newland