Hey Mike - Thats exactly what I used. My fibreglass guy gave me a bag of the talc stuff - just mix it in with the resin till it gets to the right consistency. Takes longer to go off then regular body filler so you have more time to shape. I have been using the off the self stuff for the final smoothing though, as it seems to sand a little easier.
Ill send your 10% off in the post tomorrow
Cheers.