I had an idea: add another back pack that will increase the ammount of AT ammo. It would have to have different models for each campaign (if not for each type of weapon). For example for Panzerschreck it could look like this:
It’s just a thrown idea so give your thoughts.
Ps.
Unless…
yes please
Maybe also option to have it on non-bomber soldier and add order “request AT ammo” from that soldier. So you can distribute the weight (because that backpack will be heavy) to other squad members.
this photo, i love it 
Slow the soldier down immensely that carries this for balance … and, have him explode if he gets shot ???
Yes
It will be too much penalty for too little benefit.
OMG
This is actually not an impossible idea to implement, and the reason I say this is because of the “squad” concept in game.
If you actually have a look at the anti-tank squad make up, the size expansions take you out to 6 soldiers.
Technically you can reduce the number of anti-tankers to two, and give each of them an assistant that carries the ammo reload. All they would need to implement is an ammo re-fill function from the AT soldier turning to the assistant at some reasonably close range - same mechanic as you have with the current ammo dump reload.
This would leave you with two slots arguably to be filled with an assaulter to be the squad NCO and an engineer to provide your squad with spawn anchoring flexibility and additional reloads if you have the time to do so.
It would work particularly well for the later war squads armed with Bazooka’s and PanzerSchrecks, all be it, it is completely feasible for the PIAT right now.
Fall of Berlin uses PzFausts so the game already abstracts the 4 reloads that you could “arguably” drag around.
The distinction for non-AT squad ant-tankers in other squads would be the reduced ammo availability