i have 2 bowls that "pop" off. This is what I do:
Pack bowl, place on hookah.
Wet a single sheet of papertowel - wring out.
Wrap around the bottom of the bowl where the bowl meets the stem/grommet.
Then I wrap some alum foil around the papertowel, up around the bowl and down over the papertowel. It helps keep it stable and airtight.
Reason I put the papertowel on the outside rather under or replace the grommet: these 2 bowls still "pop" off - the necks are too narrow for the top of the stem section.