xtraflyr - I wasn't aware that Slimline discouraged this, but the reasons you state are the reasons why I don't use soft mounts. I'm still fairly new to gas engines, but it just made sense to me that mounting on soft mounts would only exaggerate vibration concerns. You would think this would dampen vibration, which seems sort of rational, but it doesn't seem to work out this way from what I have read about and observed. On my Pitts I mounted a 24 oz Dubro tank for smoke with 2/3 of the tank forward of the CG and 1/3 over and behind the CG.