I noticed in the Terrain Effects Chart, the Terrain Type Town says yes for Entrenchments but know that is incorrect, as you can not place an Entrenchment counter in a town hex. Maybe this has been mentioned before?
There is no such rule that I am aware of. You can place Entrenchments in town hexes.
Older scenarios stated something like "Place Entrenchment markers in X non-town, non-wood hexes" but that practice was discontinued years ago.
Then again, I look at the Assault Chart and I am incorrect but you don't get an additional modifier for the town, only a -2 for the Entrenchment.
Learned something new.
You don't get additional modifier but you get the first fire bonus and the no fleeing if demoralized bonus.