Rubber side down
I second this. I have had the nut loosen twice since installing the Progress (stiff setting) swaybar with GRP endlinks. Once not long after initial install, the second time at the track a couple months later. I may have forgotten the loc-tite the first time, but I definitely didn't when I did the first re-tightening. The added stress at the track was enough to loosen it a second time. I re-torqued it at the track the second session and it hasn't come loose since.Just make sure the adjustment locking nuts have loc-tite on them and are as tight as you can get them.
Just remember, if you hear something that sounds like someone tapping on your subframe with a hammer (in automotive diagnostic speak, it would be considered a strong "clunk" sound), don't be too alarmed. Just check your endlink nuts, one of them is loose.