I used RTV Silicone to bed them in (warmed them up in a polythene bag dunked in hot water for a few minutes first - polythene bag to keep them dry - not sure if it had any beneficial use but do this whenever fitting any kind of rubber seal), closed the vents and left them for a couple of days for the silicone to cure properly... now been in about 3 years still nice and secure with no leakage at all