Self sticking thermometer strips are available to put on the outside of the fermentor.
I now use a digital thermometer taped to the outside of the carboy, and insulated from the room air. It was only $6.00. I replaced it for kitchen use because it was slow to show temp of baking bread.
Your crawl space could be very inconvenient for handling a filled fermentor and tracking fermentation progress. Swamp coolers are very effective. Without a fan my swamp cooler will hold the fermenting wort 6° lower than ambient room temperature during active fermentation. Adding a fan 8° to 10° depending on OG.