Another big advantage of gasoline, you can use much smaller tanks in the plane, roughly a gasoline engine will only burn half as much per unit time than a glow engine will. While you can convert a gasoline engine to glow (as mentioned above) it does create problems when doing so. The biggest one is that you need to replace the carb in order to run glow fuel in a gasser (requires larger offices and fuel passages to accomodate the increase fuel consumption). As far as vibration goes, the big glow engines vibrate as much as the gasoline engines do although the glow engine will be lighter than the gasoline engine for the same cc and will put out more power per pound of weight, just use a lot more fuel.