A Quartermaster's worst nightmare

[JonS1]

keep them trucks going only when the
moon shines? forfeiting the travel mode and let them
reach the front after the war is over?

Basically, I think this is your only solution.

Unless, you edit the scen such that the 'auto' air interdiction value is quite low AND then add the equivalent airpower as dixcrete units AND add any absent AA assets as discrete units. Then the side with the air has the option to use his airpower on CAS or deeper missions - which might see more of your trucks trucks getting to the front, and the sidfe without the air has the option of defending the MSR(s) with additional AA assets.

But even then, sticking to night and staying out of T mode is probably a good idea.

Oh, one other thought: think of the truck units as drops of water in a pipe, all contributing to the flow, rather than as point units. The most important logistic goal you have is to establish a steady flow to the front. Once that is done, it doesn't matter whether that flow only moves at night or in tactical mode. In other words, it doesn't matter how slow elements of the flow move, as long as the flow delivers enough to the front each turn to meet consumption.

The tricky bit, of course, is establishing the flow in the first place. Once that is done, the tricky bit becomes resisting the temptation to speed up some part of the flow to meet some local crisis or opportunity. If you do that, you will break the flow, and have to go through the heartache of re-establishing it.

Incidentally, the same basic adivice applies to moving combat unit reinforcements forward in the face of enemy air superiority.

attacking with whole army groups low on fuel+ammo?

That is indeed always an option, but should only be temporary, or reflective of a general breakdown of the logistics pipeline.