Sounds interesting! I like your ideas for where to place them, and using the towers as fast travel points around the corners of the map is exactly what I had in mind.
If I were prepping for my own game, I’d do a mix of having towers that are easily accessible by the players (but might require some repair) and towers that have obstacles to access or are currently occupied. It adds some fun challenge and conflict if they need to convince a bat or bee hive to let them in.
Having a tower buried inside a termite tower sounds great!