It's been so long sense I have seen a fuel foam from vibration I can't even recall when it was. The anti foaming agents work that well. There was an address for a video from Germany but it is no longer up. They have a tank hard mounted on the outside of the fuse with a camera on the wing pointed at the clear tank to show what the fuel is doing during different stunts. A true eye opener. Throughout the whole flight not one bubble in the tank. Foaming just isn't a problem these days. I just happen to have my favorite flying model with the canopy off today so I can replace the battery. Here is a photo of the tank. It's hard mounted over the CG. The plane is a CG Extra with a YS 1.20. Never even a hiccup from foaming or vibration. I have 5 other planes in my shop with the tanks hard mounted like this. I wouldn't risk any of them if there was a foaming problem and the fix was just some closed cell foam. Fuels have improved over the years and foaming is a thing of the past. A tank/line problem is something that still happens all the time and bungs don't get tighter with age.