Buying advice for weird scenario: adequate projector for holiday decorations?

I'd like to purchase a cheap/used projector to mount in a tree (protected by an overhead baffle against rain or snow) and drive the video with a Raspberry PI over HDMI to project onto a wall approximately 15' away.

I know that fixed-function outdoor holiday projectors exist but I want control over the imagery displayed. Putting my own setup together sounds like a fun project, anyway.

This would be in Wisconsin, where temperatures for Halloween are typically 30-60F and for Christmas are typically -10-30F. It is likely that this projector would only be used intermittently (only at certain times of day, and only from October to December).