Person in Armed Forces, non dependant or bedroom tax ?

I am sure this will come up alot with the new Welfare Reforem changes and myself and colleagues have been trying to find the regulations that would help with this.

Tenant has three bed RSL property and is on an income based beenfit so gets full HB.  She has two sons, one is dependant and the other is in the Army.  He is not on deployment at present but only comes back at the weekend unless away for longer for a course.

1.  Is he resident and therefore non dep applies if he only comes home most weekends
2. if he is away for longer periods but not on deployment, when does non dep apply or not
3. when / what periods does this apply to mother needing to pay bedroom tax?

i am aware of Williams v Horsham District Council [2004] EWCA Civ 39 (21 January 2004) but i do not believe this answers the questions above.

Thank you

Kat