I can not disagree about the WD-40, it does displace water. It is not too bad as a rust prohibitive/ lubricant. Just make sure you have a good protectorate on before it gets wet too, not just after. After the WD-40 dries on, re spry it with a good lubricant that will not gum up over time. Maybe it just me, but WD-40 if left alone and reapplied many times over an extended period of time (years) can build up and get gummy. I think if you keep mixing in good lubricant/rust preventative like Rem Oil or Break Free, it will not gum up and will help prevent rust, like WD-40. Of course the Handi action is not real precise. What I mean is the parts that have interaction are robust and have a lot of force to move them like on the hammer, latch and trigger so they probably would not gum up. Close fitting parts like bolt releases, that do not have a lot of force to move them can get gummed up over time, especially if not used for a while.
Enough rambling - Any gun needs to be taken down and cleaned thoroughly from time to time and a fresh rust preventive/lubricant put on. That should prevent a build up of any kind, be it gummy lubricant or dirt/powder blow back that gets attracted to the lubricant.