I am going to make a few homemade feeders. One style will be exposed to the elements all the time. What else would work good other then corn. Can't seem to find soybeans locally other than soybean meal (Maine). Is there ne thing else I could try

Try Sportsman's Choice Deer Feed Protein Pellets, they are rather expensive but mixed with corn you will see the benefits of this product by a little extra antler growth, but most of all keeping the deer healthy and keeping up a good herd.

You can use oats mixed with corn, should be cheaper than marketed deer feed.