The Key Vault appears to be well made, with very little plastic.  Being concerned about rust (which may or may not be a problem), I put a little bit of Teflon oil on the inside of the two sliding retainers that hold the two pins in, as well as a drop on the two latch points before installing.  This way, if it does get some rust, it will have less of a chance of seizing up.  Long term instead of oil, I'd probably recommend a small amount of Teflon based grease where the pin contacts the two sliders, as well as on where the sliders contact the inner wall.  Since the drawer walls are high, the oil isn't going to come into contact with the contents.  I'd probably consider a drop of oil on the spring in the back that pushes the drawer out when the right combination is entered and the lever pulled.I easily changed the combination and had no problems whatsoever installing it.  Time will tell if it gets water into the drawer, but so far, it looks decently water resistant.  I personally am not worried about water getting in the drawer.As for people being able to tell it is there, the only real way someone can find it is if they examine the hitch pins and notice that it isn't a standard hitch lock, or pull off the dust cover.If someone had to place a spare key on a vehicle, this is the most secure solution for this answer.  Of course, a thief who has some power tools can get into it, as well as someone sitting there flipping through 10,000 combinations.If someone is worried that keeping a spare key in this would be a security issue, you can do the following which an acquaintance of mine does:  Keep a "dummy" key in the Hitch Safe that will open the door.  Then inside the vehicle, use a console or other strongbox with a stout lock store in there a spare key that works in the ignition.  This way, for a thief to steal the vehicle, they would have to either break out the Hitch Safe, then try drilling out a heavy steel enclosure for the ignition key, or break the windows and try to get into the console safe.  Either way, eventually a thief would prevail, but it will take a lot of time and noise.  For all but the most crime-plagued areas, the Hitch Safe appears good enough -- it keeps all but the dedicated thieves with hand/power tools away.