I would say survivable not safe. When you start moving arty around of road I think you will make yourself a very good target because IED are going to have a greater effect slowing down or disabling artillary instead of merely hassling patrols and supply convoys. Afghanistan doesn't have the best road network reaching high into mountains where it would be ideal to place artillary. PNG also doesn't exactly excel in road networks either. Nor are bushmasters going to be quick covering mountainous/muddy ground in case of movement or withdrawal. Nor can bushmasters directly deploy from the LHD amphibiously, we are then moving them out the dock with trucks, tanks, APC's, SPA, or amoungst islands in the pacific etc.
The argument for Chinooks goes beyond moving 777's around.
I'm not arguing against the notion that we need Chinooks, clearly we do and the more the better but the points you are raising are countered by reality.
1. We do not have Chinooks or artillery in Afghanistan in direct support of Australian forces. Therefore we have precisely NO need to move any artillery capability.
2. The Chinooks that we deploy to Afghanistan join the multi-national pool of helicopters and are not soley engaged in supporting Australian forces.
3. How often are towed artillery pieces moved from fire support bases in Afghanistan? Unless you know that, you cannot with any reliability argue against a particular method of moving an artillery piece. Do you think that movements of force critical platforms are telegraphed to the enemy? Do you not think that the movement of an artillery piece would not occur with an escort? Route clearance is a principal task of armoured forces in Afghanistan, along with engineers. Any movements will be cleared as best as is possible.
Some Australian Bushmaster vehicles have been struck by IED in Afghanistan. Some special operations vehicles too. How many engineer plant vehicles have been hit though? They are too heavy to be moved by helo and must rely on transporters and yet how many have been hit by IED?
4. Australian forces are supported by a mix of self-propelled guns (Dutch PZH-2000) and towed guns. The PZH-2000 cannot be airlifted by ANY helicopter and are at risk from IED's. Apparently the threat is considered safe enough to move these though the region. Is the loss of an M777 worse than the loss of a PZH-2000?
Bushmasters and towed artillery are at risk from IED? Chinooks are at risk from direct and indirect ground fire. The maker of defensive IR systems the other day was boasting of how a Chinook fitted with same managed to fend off multiple ground launched SAM's. Is that a risk you are willing to take for Australia's precious few Chinooks?
A Chinook is a force critical platform. It deserves and is afforded the greatest amount of force protection that Army can provide it. A single towed artillery piece is not as critical.
A shot down Chinook is a FAR greater loss than a Bushmaster or even an M777A2 from an IED threat. For all the talk about air movement of artillery, by far the greatest amount of movements of these pieces happens by gun tractor.
Where appropriate, air movement or air drop will occur. Overwhelmingly however, ground movement will be used, simply because there is insufficient tactical air transport available and it is much more efficient and cost effective to do it by gun tractor.