May I ask some questions as a complete outsider? Apologies in advance if any of them are stupid. Firstly, how much warning could you realistically have expected of a Soviet attack? Secondly, how much live artillery and or mortar ammunition could have reasonably been stored against such an attack? I presume you couldn't simply have stacked the ammunition out in the open in all weathers next to the guns or mortars. Therefore I should think you'd have had to have kept it in storage and it would thus have to be unpacked and prepared for firing? Would you have been working from Fire Plans or would you have had to react to the situation as it developed?
In wartime the Allies might well have got up 1,000 rounds or more per gun (and I wouldn't doubt that they did), but surely that would all be quickly used up? My last question would be, if the Soviets had decided to attack, they would surely have very quietly and stealthily brought forward vast stocks of all kinds of ammo, from ball for the rifles to battlefield nukes even? The idea being to loose one short but massive barrage behind which would have emerged their tanks and Infantry? That at least was what Victor Suvorov posited would have happened.
A brief and rough overview:
If you mean a full attack by the group of soviet forces onto NATO Germany, then I think its now generally assumed that there'd be days or weeks of advance notice. Apart from the rising political tensions, it would take a massive logistic operation to get either Warsaw Pact or NATO forces up to fighting readiness. You are talking about motorways nose-to-tail full of HGVs, with those convoys extending for hundreds of km. NATO's biggest-ever exercise - Lionheart - only involved about half of the available land forces, and yet it took up to a week to get some units into position.
Hiding vehicles and ammo is a serious problem in a modern war - surveillance systems are a lot more capable than the WW2 equivalent of a quick overflight by a photorecce fighter. There would have been no chance of the soviets ever achieving a secret mass mobilisation and pre-dumping operation.
"First line" ammunition is stored on gun limbers - the vehicles actually in the various batteries and fire units. When engaged in firing, ammunition is unboxed and laid out/stacked on the firing point. For an arty piece, the shells and charges have to be close at hand to meet any fire order, and rapid rates of fire. Ammo'd be typically covered from the weather by a tarpaulin, but most types are fairly weatherproof anyway.
Second line ammunition (limited quantity) usually held on QM vehicles belonging to the same unit. These replenish from forward ammunition points, where ammo would typically be brought forward by RCT or similar on 10-tonne trucks - or similar, depending upon unit and army.
Arty ammo logistics would have dominated the vehicle movement plan, with POL and other munitions taking up relatively less resource.
Sufficient ammo for the likely task is prepared. Bear in mind that, in a NATO vs WP setting, arty units would likely have to move frequently and rapidly - so much ammo would have to remain on vehicles. The DROPs system was brought in to deal with the problem of having to dump large quantities of ammo, and then to pick it up and bug out as well. In WW2, ammo sometimes had to be abandoned or blown if it could not be picked up in time.
Most formation would have predetermined fireplans. As NATO in Europe was to fight a mostly defensive war, those fireplans would typically have lots of DF targets. As the situation changes, the arty commanders' job is/was to prepare fresh target lists and fireplans. Of course, fire was always on-call anyway, so tactical emergencies would simply be dealt with ad hoc.
