In your owners manual, under battery disconnection section on page 258, it states the following:
The battery may discharge if the vehicle is not used for approximately six weeks.
If the battery is disconnected it may discharge after approximately 12 weeks. Trickle feed on a battery charger overnight, before installing back into the vehicle.
If the battery is disconnected or discharged, the boot (sedan) and the tailgate (wagon) will not open normally...
(followed by info on the consequence of disconnecting a battery)
Also, I don't remember reading any further advice from Holden, related to other aspects of vehicle non use/storgae, in any other sections of the owners manual. So, about the only problems you'd have after 3 weeks of non use is .... nada... zilch... zero... according to Holden itself
And as mentioned by others, you'd not have issue even with a six week driving hiatus (though i suspect cranking would get harder as the battery got older where real old batteries may not start the car).
If you park a car long term, say more than six weeks, best to remove the battery and connect it to a quality trickle charger which will serve to avoid killing the battery through sulphation (caused by too low a battery voltage).
If your car is parked six months or more, i'd also place the car on stands so the weight of the car is not on your tyres. I'd do this to avoid getting flat spot memory effect on your tyres (though they usually work themselves round within a few hundred kays of driving).
For very long term storage, i've heard some classic enthusiests completely fill engine block with oil, including above the pistons (via temporary removing spark plugs). They do similar overfills with gearboxes, etc where possible. Obviously this is lots of work up front and also means lots of work to prepare their car for putting back on the road. I'd never bother with such extreams with normal cars. Expensive classics, maybe, but i don't see VF's being worth 100's of 1000's of dollars ant time soon....
Edited to add that keeping it out of the sun is a good idea as well... as panhead alluded to...
