Question on freeze protection for outside wood boiler

I've had a classic boiler for about 10 years now. I run it year around (Michigan), heating my house, attached garage, and a pole building. Having been retired for several years now we would like to take a month or two in the winter to find some warmer weather. My question is in regards to shutting the boiler down for an extended period. I've read online about antifreeze protection using proplyene glycol. I've also considered just draining the system and blowing the lines out. Personally, I believe that keeping the boiler full is a better option to avoid corrosion. Would a 20-30% solution be adequate if I kept the pumps running? Also is all proplyene glycol anti-freeze the same (?) as price varies considerably from different brands. Any input would be greatly appreciated. Thanks, Tater