Christy -
Since you are in Michigan, you are right in the back yard of the inventor of Rim Guard. IMO, that is the way to go on tire fill. It's non-corrosive (unlike Calcium Chloride, one of the more popular fills), non-toxic to animals (unlike most antifreeze... in fact Rim Guard has an animal food grade certification), and doesn't kill plants if you spring a leak.
I have Calcium Chloride in My TC33D rear tires. Unfortunately, I hadn't heard of Rim Guard when I had them filled. First leak I get, I'm getting them switched over to Rim Guard. If you are interested, I can probably dig up a phone number to the Rim Guard people around here somewhere...
Congrats on the new tractor!
John Mc