i have to do it again for the boost gauge. i used the same method as for making motor mounts... except i used a glass tube from work that was a hair smaller than the guages i have - for that tizzite fit. how can i smooth it out now? i know the soap trick for when you apply it... can i use a thick hobby paint as a filler and a razor blade to trim? any suggestions would be greatly appreciated. the product at hand is black RTV.