If it's a big gazebo you may want to mount it on top of a pole with a squirrel baffle, if it's smaller you could hang it on a baffled pole with some other feeders. It would have to be around 10 feet from a launching pad, depending on what that was. For example a squirrel can jump farther from a deck rail than it can from a spruce bough.
As for the rain, can you drill more holes in the tray? Sometimes with those feeders you can put an up-side-down funnel in the middle to deflect the seed to the ports and keep less of it on the "floor" of the feeder where it will get wet.
Post a couple pictures of it, maybe others or myself would have suggestions.