ive modified these pictures to help demonstrate potential garrison points.
Add firing ports to the research facility's walls, this allows garrisoned troops to shoot out, adding small guard towers to the places where the AA turrets are would also help, they can be used in lieu of turrets, or the turrets can be added to the roof of the guard tower.
harvester catwalk could use to be extended in the rear to allow more space for extra garrison soldiers to cover the rear of the vehicle
the airfield provides a high vantage for troops making it an excellent place for garrisoning, it would also be nice to have a staging area for dropship troops to wait, they can then board the next available dropship. finish the ladder in the rear of the building and allow it to connect to the raised platform for troops at an even higher altitude, would also be nice to have the ladders be usable
The refinery could also use to have the ladders fixed this would allow more elevated garrison locations. add a catwalk to the gantry beside the harvester drop-off, this gives additional garrison points. it would also be quite nice to have a drawbridge here that will connect to docked harvesters allowing for easy embarkation/disembarkation for harvester drivers.