don't really think rain would do to much damage. Just like a gun or anything else you care for, if its out in the rain or something like drop it in puddle etc etc..just bring it in that night and give er a quick wipe down and some heat to dry whatever out. if you really wanted to put something on the crossbow for the rain make sure your string is always waxed real good and just put some wd-40 on a rag and wipe some parts down like the cams or the scope and mount etc.