Wax is good, but it won't "lock" moisture per se. Only a very thick coat of modern varnish will come close, and even then it's permeable so you'll never keep moisture out. At some point, the wood is going to end up having the same RH as the air around it - it's unavoidable, but not a bad thing. If a bow is too dry it will become brittle, and of course if it's too wet it takes on excessive set.
Some woods like ash, maple and elm are very bad when they get wet, and it's always better to resist being "traditional" with waxing/oiling and just seal the bow in a modern waterproof varnish if you want the bow to last. You can apply wax over the top to dull the finish and get the feel of a waxed bow, without it constantly taking set or shooting like a damp noodle if it gets wet or the air humidity is higher than normal.
Most of the traditional finishes we know about were for yew bows, which are extremely good at being consistent in all weathers. Just because a yew bow can be waxed and oiled and not be affected by humidity doesn't mean that white woods can as well. In fact if you talk to the guys who really know their stuff when it comes to making selfbows out of whitewoods they recommend putting the bow on the radiator daily when working on them, constantly washing your hands to avoid sweat coming into contact with the wood and gently toasting then immediately sealing with modern varnishes the moment the bow is finished. None of this is necessary with woods like yew, but of course many people read about the romantic, traditional beeswax finish or boiled linseed oil / Danish oil and think it applies to all longbows!