I don't have any "good" boots but a few weeks ago, in the dead of our summer, I dried out a pair of shoes by putting next to a dehumidifier that I have running in the basement. The machine kicks out warm-ish air but it's dry, so, it works well, so it was free drying after a rain. Doesn't work in winter of course.Ive used a hair dryer to dry them out in the last, but I had to stand there while doing it, and it really sticks the house out too.
I have recirculating hot water for heat so boots usually get stacked on a register and left overnight to dry.