What is the best way to weatherproof the plastic box for a motion sensor originally intended for indoor use?

The motion sensor in question is a cheap Quorum Passive Infrared Detector (RR-150/A-160/G4567) powered by a 9V DC battery that emits 5V for about 1 sec when activated. The trick is that I also want to solder leads to the battery contacts so that I can power it using a wall transformer. It comes in a plastic box that is totally unsealed; so far I have considered either using a glue gun to seal all seams and holes, or putting the whole thing inside another plastic (or plexiglass) box. For the moment I am most concerned about water leakage, but it is possible that temperature is an issue, too, I suppose. The sensor will be used in a temporary outdoor installation for six months this summer.What is the best way to weatherproof the plastic box for a motion sensor originally intended for indoor use?Get a tube of RTV. It's a kind of silicone caulk. Try hardware stores, auto parts stores, or maybe radio shack. Apply a smooth bead to every seam and to the hole where the wiring enters the box...and about 2 inches or so of the wiring. Don't force it in to deep or it may interfere with the sensor. It goes on sort of like caulk. After you apply a bead to the seams smooth it with a wet finger. The smoothing is mostly for cosmetic reasons but will also help make a good waterproof seal. Make certain when you mount it that it is several inches off the ground, to avoid water splashing up on to it, and as much out of the weather as possible.