Aaron, I konw many do not sanitize their rental boots often, but other are using a commercial shoe sanitizer, something simlar to what bolwing ally’s use. Not sure that helps, but that is all I know.
We use Zep spray once a week to santize the inner boots. It doesnt seem to affect the boot materials at all and kills about everything. During the week, espcecially when its busy we use the Toko Eco Fresh in a spray bottle to keep the funk at bay – 4-5 times per week at the end of the day. dries quickly and leaves a fresh non-ski boot scent in the back room