It could work, but really it would be a weapon best used en-mass, unless we want to introduce 150mm-sized weapons, opening the door to abuse by mega squads.
But really, I think the Wespe, Priest, and MAYBE the Brummbar (as a high-perk assult gun) would be our best bet.
IMO, they should get a modified land-gunner mode. They click on a target on the map, and it shows the coordinates of the point they clicked on. There would be a second set of measures giving the current range and bearing of their weapon. They would have to manually aim their weapon, and correct for recoil after firing.
Results from the map are imprecise at first, but get more and more accurate the longer you hold possition.