All good points. I have squirrels, lots and lots of them. They occasionally go after the feed but it hasn't been a huge problem. I also have a lot of pecan trees, so they are kept busy with those. (I swear, when the pecans are getting close the squirrels throw them at us!! )
I did try the tube feeders made from large PVC pipe many, many years ago. They were a huge problem for me. The food was always clumping and getting stuck and clogged, and spoiling, waste was a lot. It was the condensation in the pipe, not the humidity.
And when feed starts to go bad, it gives off heat, so condensation gets worse in a closed environment, more moisture, more rapid spoilage, more heat, and so on. So I use open feeders now, either open dishes or feeders with open tops that are larger, and again, only a days worth of feed at a time.