Not exactly Bondo, but made by the same people, Dynatron Dyna De-Lite works even better.
The regular Bondo is somewhat grainy. The Dyna De-Lite has a much finer grain. I get mine from AutoZone.
Napa has a flowable glazing putty that I want to try also. Bill Geary suggests Dynatron PuttyCote, if you can find it.
Evercoat putties are generally refered to as being the best - but I've never been able to find any of their products.
Bondo Glazing Putty & Spot Filler (the red stuff) works okay, as does Acryl Blue or Red (available at NAPA stores.
Hope this helps,
Tim D.
http://modelcartech.com
Tim D.