It took me 2 tries to successfully install my SeaCure II. The mouthpiece (MP) is too small to just slide onto the DSV, so I had to heat the part of the MP that the instructions tell you not to heat. The first time I did this I heated it too much and it went right on, but I found out a few days later that it stretched too much, it actually came off during a dive (that kinda sucked) even with the zip-tie.

The second mouth piece I bought I only heated it up a minor bit and really had to work to stretch it onto the DSV. Then I zip-tied it making sure the zip-tie was very tight, then I added a second zip-tie just to really make sure it was on securely. It has now been on for over a year.

The key is to only heat the MP end slightly and really force it over the DSV.