I don't believe that will harm them. Drying and applying fungicide is a good move, but I wouldn't trim the roots. No need to create any wounds on healthy tissue (and invite pathogens). I think you're right to store them in some sort of media. I've never used sand, but I have stored bulbs in vermiculite. I think I would use the media dry rather than slightly dampened. Some tubers require some moisture in the storage media, but true bulbs like the spider lily typically store better completely dry.
