[RightDeve]

The whole of the map in SP is the front line. Rear line is where the logistical things are done by the logistic officers, where the ammo is distributed before the battle started. It is here that those ammo trucks unload themselves, where they reach the end of the supply line before going back to refill in the supply depot.
So, that is not the normal thing to have in SP, because the scope just doesn't allow that.
Even in large maps where you have artys parked with their ammo, it is still considered a special case, where the front line is near enough to the batteries.
That's why ammo trucks are treated the way they are in real life; they're not meant to be participating in an active battle. That's why they don't have complete camouflage or armor etc for a battle. If you want an ammo unit for an active battle, use ammo canisters or armored ammo carrier instead of trucks.
Anyway, ammo trucks are just trucks filled with ammunition.

...

or maybe what you meant was that the ammo truck should not be listed as such in the Unit Info Screen lest the enemy opens it up? That way, the enemy will just see them as normal trucks and won't be as hungry for them than if they're ammo trucks?
If that's the case, well, it's a matter of changing the game code. I believe that'll be a nice change, but somehow difficult to implement for the developers, maybe...