Yeah. the campfire warding off the darkness and creating warmth and shelter is one of the oldest things we as humanity have. I don't think it would be worth much of anything on its own, but I would let the metaphysical symbolism of that work with Bless This House.
From my perspective (and this comes from someone who has spent many a night with others around a campfire...) a campfire would not really 'count' as a Threshold.
From both canon and RAW, one of the Thresholds is the transition from night into day (or vice versa), darkness transitioning into light is not one of the mentioned Thresholds. Midnight and Midday are also Thresholds, depending on who/what is involved. There is a reference in Changes that midday is a point of transition for the Unseelie Court, with True Seemings transforming back to their original forms at this time. There is also the inference that midnight is a similar time for the Seelie Court. These points of metaphysical transition seem to act as Thresholds vs. Seelie or Unseelie magic, depending on which time is involved, and there is no mention or requirement that actual darkness or light is required. The same also applies for the transition between day and night, or night and day. Of course exposure to direct sunlight from a rising sun has been mentioned as having a greater impact upon the weakening of latent spells like Wards, even things not exposed to daylight get progressively weaker as days keep transitioning.
One of the other often mentioned factors involving Thresholds, is a physical structure or barrier, along with the intent of the builder or builders if the structure is artificial. Namely the structure like a building keeping people, things and the weather 'out', or a wall or fencing to keep things 'in'. A campfire provides no such structure.
Lastly, there is the nature of the shelter our forebearers took around campfires. Such fires provided warm from cold environments as well as a means to cook food. Animals tended to give campfires a wide berth because their only other experiences with fire would be wild fires, also the sights, sounds and smells coming from around a campfire would all include humans, an apex predator. Now animals, even predatory ones like bears, wolves and big cats do not normally prey upon people, instead considering people a threat. A supernatural nasty on the other hand might look at people (particularly en masse) as a potential threat, but also as 'food'. With that in mind, while fire is a potential supernatural 'cleanser' a campfire might act as more of a beacon to supernatural predators, a supernatural equivalent to billboard sign saying, 'Eat here..."
Of course go with whatever works for your own game.
-Cheers
