Meadrian,
Is it possible to put up siding on three sides of the pedestal?  Even some thin plywood, sheet metal, even some sort of tarp  to keep the blowing rain out would do the trick.    The feeder is only 11" square but the treadle sticks out another 7 inches in front and another 1 inch on each side.
It might be possible to build a little box that set over and around the feeder itself.   Or I could come up with a feeder for exterior use.  Maybe change the door swing mechanism so I can extend the sides out at least a foot and add an extended roof to shed rain water.  It would be larger and heavier to ship but shouldn't add that much to the delivered cost, maybe 20%?
Let me see what I can come up with next week for an outdoor style feeder.   Thanks for all the feedback.