HI Akira Yes i know what you mean about using automotive bellows, i used them as you said in the big 12ft Gato sub and they do work quite well. I am supprized nobody has made any bellows from silicone rubber, but allot of the smaller bellowsare not as good as they was a few years ago. I have not took the small Gato out for a few months now, i don't think i have took the big Gato out for 5 years now or so seems a bit of a shame as it just sits in the garage gathering dust, i ran it up a few months ago and it all works fine resin why i ran i up was i changed the coolant for the compressor Thanks for reply all the best Sub John