I can think of two ways of doing this:
A) a slightly different tank with a high pressure flame thrower.
B) make the submachine gun in the tank swapable with other weapons.
Personaly, I prefer the latter, as it increases customizability. Why not let the player exchange the smg with a pistol... or a rocket launcher...
The current flame thrower is a bit weak beacause it cannot be upgraded. A slight increase in range an damage should do the trick
