hard to say, would depend where you are (snow and cold would make it impossible here) and what "covered" means. Some other obvious ones are insects (i.e. getting in the projector), animals (birds, raccons, squirels...), burglars, heat, dust, polution.

The best (easiest) solution would be to bring it in when used, but if not I would either buy or build an enclosure for it. For example [Link: tempestlighting.com]