ORIGINAL: ual767
Jack, I would be concerned about adding an extra 4oz. The Aeropoxy will hold that firewall just fine. In fact, the soft mount is not going to do much for you except add some weight. It is a good product but I don't think you have the weight to spare. I know a friend flying the Impact with the Axi F3A and it was flying at 11 1/2lbs so it is tough to make weight with this combo. Although even at 11 1/2lbs it flies fantastic.
OK, I will trust the AeroPoxy (it's been good to me so far, that stuff dries like iron). I am trying the softmount mainly because I see it in their manual. They have one for the Hacker (the ring in the rear is basically a vibration dampener) and Pletty (they include rubber even) so I assumed (perhaps incorrectly) that it was mandatory. I fly nothing but electrics and I have had issues in the past with glass fuses resonating at a specific RPM, the soft-mount seems like a decent idea and worth a try though if it proves a hassle or a problem in itself, I can replace the soft-mount with rods (though in the end the 1.5 ounces it weighs will just be offset by rods and longer bolts)...
Jack