when you put the ideatech silicone bags between your back and the back of a chair - and probably equivalently lie down in bed or on the couch with it somewhere against your body - it can definitely very slowly leak from the main chamber into the space where the kind of strip thingie is pressed into the groove, and from there it can slowly leak little amounts of content to the outside.

I've been worried this might happen, and I'm not entirely sure how to deal with it.

If the content never has to be changed again, which is hopefully, and probably, the case, then maybe using a sowing machine to make a tight row of stitches just above the sealing mechanism may be good. On the other hand, stitching makes holes, and any content that goes through the seal may then be pressed out through the holes, or seep through the thread itself ...