yeah, those rings are rather important.

and it's a royal pain to get that bottom seal back on correctly. I did read once that you can flip them upside down (so the wick-slots are facing toward the mouthpiece) and put 'em in that way. I tried that, and it does seem to work for the most part.
The other habit I've gotten into is to not fill them past the bottom of the heat-shrink (the black bit just below the atty cup). Seems to cut down GREATLY on the seepage issue (
juice getting into the air tube) when you lay them on their side.
I actually prefer filling via syringe... even when I was using cartridges, I'd fill 'em using a syringe.