Why not make it a BR3.0 APC in the tech tree and give it a machine gun? There were armed versions with a .50cal Machine gun (wiki says 1 in 4 vehicles were armed in an assault formation), to support the landing troops.
I find it weird that Enlisted jumped directly to heavy tanks, but didn’t put extra vehicles like APCs, halftracks and armored cars as tech tree unlockable vehicles.
Br3 would be too high even if it had a 50cal, for example the soviet premium M3 half track has more armour and a 50cal, but the soviet M3 is only br2. So I wouldn’t mind if the DUKW truck got a 50cal mg but it should still be br2.
Honestly, I would move all of the armed transport vehicles to BR3.0. I think it would bring more balance to the game and the BR system, while the unarmed versions are sitting at BR2.0. The Japanese premium one is more deadly, since it mounts 3 MGs and can wipe out squads in a well-executioned assault before you can fire back.