With what skill checks, and for how long, do a siege regiment 'dig in' - with the issue of the entrenching tool and sandbags they're clearly intended to do so.
Equally, should there be some sort of 'bolster defences' type talent? Something Sarge can do to direct a squad digging in and earn them an extra armour point or two?
Suggest a possible specialisation of Trade (Pioneer) to cover digging trenchworks, laying razorwire, etc, etc.