The point of having two tons of ammo here is not endurance, it is flexibility. If it only had one ton of ammo you would have to choose between standard and Inferno rounds at the start of the match and be stuck with them, but with two tons you have the flexibility to pull a finishing critseeking strike against a damaged 'Mech or torch an unlucky tank depending on what is needed at the moment.
Harasser 3070- 25 Tons, 10/15 Fuel Cell engine, Armor (3.5 tons standard) F 15, L/R 9, B 8, T 15, 4x MML-3 (T), 1 ton MML LRM ammo, 2 tons MML SRM ammo, 482 BV, 1,042,500 C-bills.
<3 Fuel Cell engines. That's a cheap-o version, you could swap to HFFA armor for a little higher cost and better battlefield endurance, but at least that one can take a shot to the front or turret from even a big gun and keep going. And you could mix up the MML ammo, of course. Want a ton of Inferno or Thunder rounds, it's got the room.
And yeah, an extended-range LRM rack wouldn't work badly with these either...once they're out of the prototype stage.