i use epoxy fairly regular - if you are getting 'holes' forming and
fiiling with dust when sanding - i have found the holes are not formed
by the heat of sanding - the holes are formed from the heat of reaction
when the epoxy starts to set. to limit the bubbles try not to use to
deep a fill of epoxy. the thinner it is (3-4mm) the better and less
likely to get bubbles. also when mixing try not to mix vigoursly - fold
the two parts together.....

good luck