Ya some thread locker should be easy enough. The reason there are two I believe is after you tighten the first one, then snug the 2nd beside it, that should keep em tight together?
You MUST tighten the FIRST nut (the one on the inside) ALL THE WAY down tell its tight. Then when finished with the first proceed to tighten the second nut snugly against the first one. If you do not do it like this what you have described will happen. If they are coming loose and you are doing this you need to make it tighter…
make it more tight or maybe you stripped it... There really shoudlnt be a problem with this; if you must use thread locker use locktite red - nothing higher.