Thanks for posting that Harry.
The best results I've had have come from a tip given by another poster on there who was quoting Burt Rutan:
"The bottom layer should be an epoxy "slurry" consisting of a loose mixture of microballoons and epoxy"
I've used cabosil for that rather than microballoons but, given that he's building airframes, microballons make more sense to keep the weight down.
As far as the temps go, I do agree with a lighter color but for a it of a different reason. Dark hulls in warmer latitudes have an obvious tendency to warm up, which will soften the epoxy.
I also play around a bit with knifemaking and when I want to change handle scales I've glued on, I just boil them. Boiling water doesn't hurt the blade's temper but once the steel warms up those scales fall right off without leaving a residue on the tang.
I wouldn't think there would be enough heat transfer through the layup to warm the foam to melting temp, especially since the epoxy itself would begin to be compromised at a temperature of a coffee in a styrofoam cup.
I would be more concerned about foam damage from exotherm stacking during layup. If you apply another unit (layer) over one that's kicking off, it will accelerate the gel time. Towards the end of the gel period is when the most heat seems to be given off. That's (for me at least) about the time it takes to get the next unit on. Now you've got two exothermic reactions at the same time and the foam's R value is allowing that heat to dissipate through only one side of the layup. That's a perfect recipe for blisters.
I've had runaway layups that have actually started smoking, I've seen melted mixing pots and I've had one shop catch fire (though that was from a glasser leaving a pot of catalyzed vinylester in a cabinet).
I will be using multiple units over blue foam on mine, so this is definitely something to think about, but I wouldn't call it an insurmountable obstacle.
Then again, I'm not an expert...just a long winded amateur !
GPW, you aren't suggesting we stop trying ways to make foamies better are you ?!?